From 739f6759f5620a012bf3f5b34981c85db3af72e5 Mon Sep 17 00:00:00 2001
From: Aolin <aolinz@outlook.com>
Date: Fri, 12 Jan 2024 21:28:07 +0800
Subject: [PATCH] blog: Get an Integer from a String Using stringstream (#60)

---
 .../2023-03-19-cpp-beginner-guess-number.md   | 415 +++++++-------
 website/blog/2023-09-04-cpp-beginner-cmake.md |   3 +-
 ...2-cpp-beginner-stringtoint-stringstream.md | 306 ++++++++++
 website/docs/cpp/cpp-wiki.md                  |  99 ++--
 website/docs/cpp/guess-number.md              | 542 ++++++++++++++++++
 website/docs/cpp/stringtoint-stringstream.md  | 302 ++++++++++
 6 files changed, 1399 insertions(+), 268 deletions(-)
 create mode 100644 website/blog/2024-01-12-cpp-beginner-stringtoint-stringstream.md
 create mode 100644 website/docs/cpp/guess-number.md
 create mode 100644 website/docs/cpp/stringtoint-stringstream.md

diff --git a/website/blog/2023-03-19-cpp-beginner-guess-number.md b/website/blog/2023-03-19-cpp-beginner-guess-number.md
index 6a37b4f..47c8fa7 100644
--- a/website/blog/2023-03-19-cpp-beginner-guess-number.md
+++ b/website/blog/2023-03-19-cpp-beginner-guess-number.md
@@ -85,11 +85,11 @@ C++ 中的输入输出可以通过 [`std::cin`](https://en.cppreference.com/w/cp
 ```cpp title="io.cpp"
 #include <iostream>
 
-int main(){
-    int a, b;
-    std::cout << "Enter two numbers: ";
-    std::cin >> a >> b;
-    std::cout << "The numbers you entered are: " << a << " and " << b << '\n';
+int main() {
+  int a, b;
+  std::cout << "Enter two numbers: ";
+  std::cin >> a >> b;
+  std::cout << "The numbers you entered are: " << a << " and " << b << '\n';
 }
 ```
 
@@ -137,11 +137,9 @@ int a = 5;
 ```cpp
 if (condition1) {
   // do this if condition1 is true
-}
-else if (condition2) {
+} else if (condition2) {
   // else this id condition2 is true
-}
-else {
+} else {
   // otherwise do this
 }
 ```
@@ -151,23 +149,17 @@ else {
 ```cpp title="condition.cpp"
 #include <iostream>
 
-int main()
-{
-    int i = 0;
-    std::cout << "Enter a number: ";
-    std::cin >> i;
-    if (i == 0)
-    {
-        std::cout << "zero\n";
-    }
-    else if (i > 0)
-    {
-        std::cout << "positive\n";
-    }
-    else
-    {
-        std::cout << "negative\n";
-    }
+int main() {
+  int i = 0;
+  std::cout << "Enter a number: ";
+  std::cin >> i;
+  if (i == 0) {
+    std::cout << "zero\n";
+  } else if (i > 0) {
+    std::cout << "positive\n";
+  } else {
+    std::cout << "negative\n";
+  }
 }
 ```
 
@@ -198,13 +190,15 @@ C++ 中的循环语句可以通过 `while`、`do while` 和 `for` 关键字来
 #include <iostream>
 
 int main() {
-    int i = 5;
-    while (i < 10) {
-        std::cout << i << ' ';
-        i = i + 1;
-    }
+  int i = 5;
+  while (i < 10) {
+    std::cout << i << ' ';
+    i = i + 1;
+  }
 }
 ```
+<codapi-snippet sandbox="cpp" init-delay="500">
+</codapi-snippet>
 
 ### `do ... while`
 
@@ -214,13 +208,15 @@ int main() {
 #include <iostream>
 
 int main() {
-    int i = 10;
-    do {
-        std::cout << i << ' ';
-        i = i + 1;
-    } while (i < 10);
+  int i = 10;
+  do {
+    std::cout << i << ' ';
+    i = i + 1;
+  } while (i < 10);
 }
 ```
+<codapi-snippet sandbox="cpp" init-delay="500">
+</codapi-snippet>
 
 #### `for`
 
@@ -230,11 +226,14 @@ int main() {
 #include <iostream>
 
 int main() {
-    for (int i = 5; i < 10; i = i + 1) {
-        std::cout << i << ' ';
-        }
+  for (int i = 5; i < 10; i = i + 1) {
+    std::cout << i << ' ';
+  }
 }
 ```
+<codapi-snippet sandbox="cpp" init-delay="500">
+</codapi-snippet>
+
 
 ## 实践：猜数字游戏
 
@@ -270,16 +269,17 @@ int main() {
 // highlight-next-line
 #include <random>
 
-int main()
-{
-    std::random_device rd;
-    std::mt19937 gen(rd());
-    std::uniform_int_distribution<> distrib(1, 100);
-    int answer = distrib(gen);
+int main() {
+  std::random_device rd;
+  std::mt19937 gen(rd());
+  std::uniform_int_distribution<> distrib(1, 100);
+  int answer = distrib(gen);
 
-    std::cout << "The answer is: " << answer;
+  std::cout << "The answer is: " << answer;
 }
 ```
+<codapi-snippet sandbox="cpp" init-delay="500">
+</codapi-snippet>
 
 ### 处理用户输入
 
@@ -289,24 +289,25 @@ int main()
 #include <iostream>
 #include <random>
 
-int main()
-{
-    std::random_device rd;
-    std::mt19937 gen(rd());
-    std::uniform_int_distribution<> distrib(1, 100);
-    int answer = distrib(gen);
+int main() {
+  std::random_device rd;
+  std::mt19937 gen(rd());
+  std::uniform_int_distribution<> distrib(1, 100);
+  int answer = distrib(gen);
 
-    std::cout << "The answer is: " << answer << '\n';
+  std::cout << "The answer is: " << answer << '\n';
 
-    // highlight-start
-    int guess_number;
-    std::cout << "Guess the number: ";
-    std::cin >> guess_number;
-    // highlight-end
+  // highlight-start
+  int guess_number;
+  std::cout << "Guess the number: ";
+  std::cin >> guess_number;
+  // highlight-end
 
-    std::cout << "The guess_number is: " << guess_number << '\n';
+  std::cout << "The guess_number is: " << guess_number << '\n';
 }
 ```
+<codapi-snippet sandbox="cpp" init-delay="500">
+</codapi-snippet>
 
 ### 判断用户输入的数字是否正确
 
@@ -316,35 +317,29 @@ int main()
 #include <iostream>
 #include <random>
 
-int main()
-{
-    std::random_device rd;
-    std::mt19937 gen(rd());
-    std::uniform_int_distribution<> distrib(1, 100);
-    int answer = distrib(gen);
-
-    std::cout << "The answer is: " << answer << '\n';
-
-    int guess_number;
-    std::cout << "Guess the number: ";
-    std::cin >> guess_number;
-
-    std::cout << "The guess_number is: " << guess_number << '\n';
-
-    // highlight-start
-    if (guess_number == answer)
-    {
-        std::cout << "Congratulations!\n";
-    }
-    else if (guess_number < answer)
-    {
-        std::cout << "Guess a higher number!\n";
-    }
-    else
-    {
-        std::cout << "Guess a lower number!\n";
-    }
-    // highlight-end
+int main() {
+  std::random_device rd;
+  std::mt19937 gen(rd());
+  std::uniform_int_distribution<> distrib(1, 100);
+  int answer = distrib(gen);
+
+  std::cout << "The answer is: " << answer << '\n';
+
+  int guess_number;
+  std::cout << "Guess the number: ";
+  std::cin >> guess_number;
+
+  std::cout << "The guess_number is: " << guess_number << '\n';
+
+  // highlight-start
+  if (guess_number == answer) {
+    std::cout << "Congratulations!\n";
+  } else if (guess_number < answer) {
+    std::cout << "Guess a higher number!\n";
+  } else {
+    std::cout << "Guess a lower number!\n";
+  }
+  // highlight-end
 }
 ```
 
@@ -356,37 +351,30 @@ int main()
 #include <iostream>
 #include <random>
 
-int main()
-{
-    std::random_device rd;
-    std::mt19937 gen(rd());
-    std::uniform_int_distribution<> distrib(1, 100);
-    int answer = distrib(gen);
-
-    std::cout << "The answer is: " << answer << '\n';
-
-    // highlight-next-line
-    while (true)
-    {
-        int guess_number;
-        std::cout << "Guess the number: ";
-        std::cin >> guess_number;
-
-        if (guess_number == answer)
-        {
-            std::cout << "Congratulations!\n";
-            // highlight-next-line
-            break;
-        }
-        else if (guess_number < answer)
-        {
-            std::cout << "Guess a higher number!\n";
-        }
-        else
-        {
-            std::cout << "Guess a lower number!\n";
-        }
+int main() {
+  std::random_device rd;
+  std::mt19937 gen(rd());
+  std::uniform_int_distribution<> distrib(1, 100);
+  int answer = distrib(gen);
+
+  std::cout << "The answer is: " << answer << '\n';
+
+  // highlight-next-line
+  while (true) {
+    int guess_number;
+    std::cout << "Guess the number: ";
+    std::cin >> guess_number;
+
+    if (guess_number == answer) {
+      std::cout << "Congratulations!\n";
+      // highlight-next-line
+      break;
+    } else if (guess_number < answer) {
+      std::cout << "Guess a higher number!\n";
+    } else {
+      std::cout << "Guess a lower number!\n";
     }
+  }
 }
 ```
 
@@ -414,46 +402,41 @@ g++ --std=c++20 guess_number.cpp && ./a.out
 #include <iostream>
 #include <random>
 
-int main()
-{
-    // highlight-start
-    int min_val = 1;
-    int max_val = 100;
-    // highlight-end
-    std::random_device rd;
-    std::mt19937 gen(rd());
-    // highlight-next-line
-    std::uniform_int_distribution<> distrib(min_val, max_val);
-    int answer = distrib(gen);
-
-    std::cout << "The answer is: " << answer << '\n';
-
-    while (true)
-    {
-        int guess_number;
-        std::cout << "Guess the number: ";
-        std::cin >> guess_number;
-
-        if (guess_number == answer)
-        {
-            std::cout << "Congratulations!\n";
-            break;
-        }
-        else if (guess_number < answer)
-        {
-            // highlight-start
-            min_val = guess_number + 1;
-            std::cout << "Guess the number from " << min_val << " to " << max_val << '\n';
-            // highlight-end
-        }
-        else
-        {
-            // highlight-start
-            max_val = guess_number - 1;
-            std::cout << "Guess the number from " << min_val << " to " << max_val << '\n';
-            // highlight-end
-        }
+int main() {
+  // highlight-start
+  int min_val = 1;
+  int max_val = 100;
+  // highlight-end
+  std::random_device rd;
+  std::mt19937 gen(rd());
+  // highlight-next-line
+  std::uniform_int_distribution<> distrib(min_val, max_val);
+  int answer = distrib(gen);
+
+  std::cout << "The answer is: " << answer << '\n';
+
+  while (true) {
+    int guess_number;
+    std::cout << "Guess the number: ";
+    std::cin >> guess_number;
+
+    if (guess_number == answer) {
+      std::cout << "Congratulations!\n";
+      break;
+    } else if (guess_number < answer) {
+      // highlight-start
+      min_val = guess_number + 1;
+      std::cout << "Guess the number from " << min_val << " to " << max_val
+                << '\n';
+      // highlight-end
+    } else {
+      // highlight-start
+      max_val = guess_number - 1;
+      std::cout << "Guess the number from " << min_val << " to " << max_val
+                << '\n';
+      // highlight-end
     }
+  }
 }
 ```
 
@@ -478,41 +461,36 @@ g++ --std=c++20 guess_number.cpp && ./a.out
 #include <iostream>
 #include <random>
 
-int main()
-{
-    int min_val = 1;
-    int max_val = 100;
-    std::random_device rd;
-    std::mt19937 gen(rd());
-    std::uniform_int_distribution<> distrib(min_val, max_val);
-    int answer = distrib(gen);
-
-    std::cout << "The answer is: " << answer << '\n';
-
-    while (true)
-    {
-        int guess_number;
-        std::cout << "Guess the number: ";
-        std::cin >> guess_number;
-
-        if (guess_number == answer)
-        {
-            std::cout << "Congratulations!\n";
-            break;
-        }
-        else if (guess_number < answer)
-        {
-            // highlight-next-line
-            min_val = guess_number < min_val ? min_val : guess_number + 1;
-            std::cout << "Guess the number from " << min_val << " to " << max_val << '\n';
-        }
-        else
-        {
-            // highlight-next-line
-            max_val = guess_number > max_val ? max_val : guess_number - 1;
-            std::cout << "Guess the number from " << min_val << " to " << max_val << '\n';
-        }
+int main() {
+  int min_val = 1;
+  int max_val = 100;
+  std::random_device rd;
+  std::mt19937 gen(rd());
+  std::uniform_int_distribution<> distrib(min_val, max_val);
+  int answer = distrib(gen);
+
+  std::cout << "The answer is: " << answer << '\n';
+
+  while (true) {
+    int guess_number;
+    std::cout << "Guess the number: ";
+    std::cin >> guess_number;
+
+    if (guess_number == answer) {
+      std::cout << "Congratulations!\n";
+      break;
+    } else if (guess_number < answer) {
+      // highlight-next-line
+      min_val = guess_number < min_val ? min_val : guess_number + 1;
+      std::cout << "Guess the number from " << min_val << " to " << max_val
+                << '\n';
+    } else {
+      // highlight-next-line
+      max_val = guess_number > max_val ? max_val : guess_number - 1;
+      std::cout << "Guess the number from " << min_val << " to " << max_val
+                << '\n';
     }
+  }
 }
 ```
 
@@ -537,36 +515,31 @@ g++ --std=c++20 guess_number.cpp && ./a.out
 #include <iostream>
 #include <random>
 
-int main()
-{
-    int min_val = 1;
-    int max_val = 100;
-    std::random_device rd;
-    std::mt19937 gen(rd());
-    std::uniform_int_distribution<> distrib(min_val, max_val);
-    int answer = distrib(gen);
-
-    while (true)
-    {
-        int guess_number;
-        std::cout << "Guess the number: ";
-        std::cin >> guess_number;
-
-        if (guess_number == answer)
-        {
-            std::cout << "Congratulations!\n";
-            break;
-        }
-        else if (guess_number < answer)
-        {
-            min_val = guess_number < min_val ? min_val : guess_number + 1;
-            std::cout << "Guess the number from " << min_val << " to " << max_val << '\n';
-        }
-        else
-        {
-            max_val = guess_number > max_val ? max_val : guess_number - 1;
-            std::cout << "Guess the number from " << min_val << " to " << max_val << '\n';
-        }
+int main() {
+  int min_val = 1;
+  int max_val = 100;
+  std::random_device rd;
+  std::mt19937 gen(rd());
+  std::uniform_int_distribution<> distrib(min_val, max_val);
+  int answer = distrib(gen);
+
+  while (true) {
+    int guess_number;
+    std::cout << "Guess the number: ";
+    std::cin >> guess_number;
+
+    if (guess_number == answer) {
+      std::cout << "Congratulations!\n";
+      break;
+    } else if (guess_number < answer) {
+      min_val = guess_number < min_val ? min_val : guess_number + 1;
+      std::cout << "Guess the number from " << min_val << " to " << max_val
+                << '\n';
+    } else {
+      max_val = guess_number > max_val ? max_val : guess_number - 1;
+      std::cout << "Guess the number from " << min_val << " to " << max_val
+                << '\n';
     }
+  }
 }
 ```
diff --git a/website/blog/2023-09-04-cpp-beginner-cmake.md b/website/blog/2023-09-04-cpp-beginner-cmake.md
index 4a6d3bc..29de2ab 100644
--- a/website/blog/2023-09-04-cpp-beginner-cmake.md
+++ b/website/blog/2023-09-04-cpp-beginner-cmake.md
@@ -229,8 +229,9 @@ target_link_libraries(hello fmt::fmt)
 下面示例代码使用了 `std::cout`、`fmt::print` 和 `fmt::println` 三种方式进行字符串的输出：
 
 ```cpp title="cpp_learning/hacking_cpp/hello.cpp"
-#include <iostream>
 #include <fmt/format.h>
+
+#include <iostream>
 int main() {
   std::cout << "std::cout: Hello World\n";
   fmt::print("fmt::print: Hello!");
diff --git a/website/blog/2024-01-12-cpp-beginner-stringtoint-stringstream.md b/website/blog/2024-01-12-cpp-beginner-stringtoint-stringstream.md
new file mode 100644
index 0000000..3b8b871
--- /dev/null
+++ b/website/blog/2024-01-12-cpp-beginner-stringtoint-stringstream.md
@@ -0,0 +1,306 @@
+---
+slug: 2024-01-12-cpp-beginner-stringtoint-stringstream
+title: "C++ Beginner's Guide: Get an Integer from a String Using string stream"
+authors: [Oreo]
+tags: [C++, CS106L]
+---
+
+```mdx-code-block
+import Tabs from '@theme/Tabs';
+import TabItem from '@theme/TabItem';
+```
+
+During the CS 106L course, I learned a lot of C++ streams. This document describes how to use [`basic_stringstream`](https://en.cppreference.com/w/cpp/io/basic_stringstream) to get an integer from a string.
+
+:::info quote
+
+The basic unit of communication between a program and its environment is a _stream_. A stream is a channel between a _source_ and _destination_ which allows the source to push formatted data to the destination.
+
+—— [CS 106L Course Reader](https://web.stanford.edu/class/cs106l/full_course_reader.pdf)
+
+:::
+
+<!--truncate-->
+
+## Overview of string stream
+
+To create a string stream, we need to include the `<sstream>` header file. Then, we can create a string stream object using the following code:
+
+```cpp
+#include <sstream>
+
+int main() {
+  std::istringstream iss("9.15 pounds.");
+  std::ostringstream oss("The price of the shirt is ");
+}
+```
+
+For C++ beginners, we usually use `std::cin` to get input from the user and use `std::cout` to output something to the console. Here, `std::cin` and `std::cout` are both streams. The following is an example:
+
+```cpp
+#include <iostream>
+
+int main() {
+  int value;
+  std::cin >> value;
+  std::cout << value << std::endl;
+}
+```
+
+In the preceding example, `>>` is the stream **extraction** operator, and `<<` is the stream **insertion** operator. For string streams, we also use `>>` and `<<` to extract and insert data.
+
+To extract the price and unit from the string stream `iss`, use the following code:
+
+<Tabs>
+  <TabItem value="extract-price-double-code" label="Extract price (double) and unit">
+  
+  ```cpp
+  #include <iostream>
+  #include <sstream>
+  
+  int main() {
+    std::istringstream iss("9.15 pounds.");
+    std::ostringstream oss("The price of the shirt is ");
+    double price;
+    std::string unit;
+    iss >> price >> unit;
+    std::cout << oss.str() << price << " " << unit << std::endl;
+  }
+  ```
+  <codapi-snippet sandbox="cpp" init-delay="500">
+  </codapi-snippet>
+
+  </TabItem>
+  <TabItem value="extract-price-double-output" label="Output">
+  
+  ```text
+  The price of the shirt is 9.15 pounds.
+  ```
+
+  </TabItem>
+</Tabs>
+
+What is the behavior of `iss >> price >> unit`? We can modify the type of `price` to `int` and see what happens:
+
+<Tabs>
+  <TabItem value="extract-price-int-code" label="Extract price (int) and unit">
+  
+  ```cpp
+  #include <iostream>
+  #include <sstream>
+  
+  int main() {
+    std::istringstream iss("9.15 pounds.");
+    std::ostringstream oss("The price of the shirt is ");
+    // highlight-next-line
+    int price;
+    std::string unit;
+    iss >> price >> unit;
+    std::cout << oss.str() << price << " " << unit << std::endl;
+  }
+  ```
+  <codapi-snippet sandbox="cpp" init-delay="500">
+  </codapi-snippet>
+
+  </TabItem>
+  <TabItem value="extract-price-int-output" label="Output">
+  
+  ```text
+  The price of the shirt is 9 .15
+  ```
+
+  </TabItem>
+</Tabs>
+
+The output shows that the value of `price` is `9`, and the value of `unit` is `.15`. This is because the `>>` operator will stop extracting data when it encounters a whitespace or an invalid character for the type. In this case, the `>>` operator in `iss >> price` stops extracting data at `.`. Then, the `>>` operator in `iss >> unit` extracts `.15` into `unit` and stops extracting data at ` `.
+
+## Implement `stringToInteger()` without error-checking
+
+Now, we can use `>>` to extract an integer from a string. Let's implement a function `stringToInteger()` to convert a string to an integer. The code is as follows:
+
+<Tabs>
+  <TabItem value="string-to-int-first" label="Extract an integer from a string">
+  
+  ```cpp name="stringToInteger.cpp"
+  #include <iostream>
+  #include <sstream>
+  
+  int stringToInteger(const std::string& str) {
+    std::istringstream iss(str);
+    int value;
+    iss >> value;
+    return value;
+  }
+  
+  int main() {
+    std::string str = "123";
+    int value = stringToInteger(str);
+    std::cout << "The value is: " << value << std::endl;
+  }
+  ```
+  <codapi-snippet sandbox="cpp" init-delay="500">
+  </codapi-snippet>
+
+  </TabItem>
+  <TabItem value="string-to-int-first-output" label="Output">
+  
+  ```text
+  The value is: 123
+  ```
+
+  </TabItem>
+</Tabs>
+
+## Stream state
+
+What if the string contains invalid characters? For example, the string `"123abc"` contains non-numeric characters. In this case, the `>>` operator stops extracting data at `a`. Then, the value of `value` will be `123`. However, we want to return an error message to the user. To do this, we need to check whether any error occurs during the extraction process.
+
+A new concept is introduced here: **stream state**. There are four stream states:
+
+- **good**: no error occurs. The I/O operations are available.
+- **eof**: reaching the **end of the stream**.
+- **fail**: the input/output operation failed and all future operations frozen, such as the type mismatch.
+- **bad**: **irrecoverable** stream error. For example, the file you are reading is deleted suddenly.
+
+To check the stream state, we can use the `good()`, `eof()`, `fail()`, and `bad()` functions. The following shows some examples:
+
+<Tabs>
+  <TabItem value="stream-state-code" label="Check stream state">
+  
+  ```cpp
+  #include <iostream>
+  #include <sstream>
+  #include <vector>
+  
+  void get_stream_state(std::istringstream &iss) {
+    if (iss.good()) {
+      std::cout << "G";
+    }
+    if (iss.eof()) {
+      std::cout << "E";
+    }
+    if (iss.fail()) {
+      std::cout << "F";
+    }
+    if (iss.bad()) {
+      std::cout << "B";
+    }
+    std::cout << std::endl;
+  }
+  
+  int stringToInteger(const std::string &str) {
+    std::istringstream iss(str);
+    std::cout << "Before: ";
+    get_stream_state(iss);
+    int value;
+    iss >> value;
+    std::cout << "After: ";
+    get_stream_state(iss);
+    return value;
+  }
+  
+  int main() {
+    std::vector<std::string> test_strings{"123", "123abc", "abc123", ""};
+    for (const auto &str : test_strings) {
+      std::cout << "stringToInteger(\"" << str << "\"):\n"
+                << stringToInteger(str) << std::endl;
+    }
+  }
+  ```
+  <codapi-snippet sandbox="cpp" init-delay="500">
+  </codapi-snippet>
+
+  </TabItem>
+  <TabItem value="stream-state-output" label="Output">
+  
+  ```text
+  stringToInteger("123"):
+  Before: G
+  After: E
+  123
+  stringToInteger("123abc"):
+  Before: G
+  After: G
+  123
+  stringToInteger("abc123"):
+  Before: G
+  After: F
+  0 # undefined behavior
+  stringToInteger(""):
+  Before: G
+  After: EF
+  -514166240 # undefined behavior
+  ```
+
+  </TabItem>
+</Tabs>
+
+## Implement `stringToInteger()` with error-checking
+
+Using the stream state, we can implement `stringToInteger()` with error-checking. From the preceding example, to ensure that the string only contains numeric characters, we need to consider the following cases:
+
+- After the extraction, the stream state is `good` : the string might contain non-numeric characters after the number.
+- After the extraction, the stream state is `fail`: the string contains non-numeric characters before the number.
+
+The following code shows how to implement `stringToInteger()` with error-checking:
+
+```cpp name="stringToInteger.cpp"
+#include <iostream>
+#include <sstream>
+
+int stringToInteger(const std::string &str) {
+  std::istringstream iss(str);
+  int result;
+  // highlight-start
+  char remain;  // Record remaining characters after the integer
+  iss >> result;
+  if (iss.fail() || iss.bad()) {
+    throw std::domain_error("The string does not start with an integer.");
+  }
+  iss >> remain;
+  if (!iss.fail()) {
+    throw std::domain_error(
+        "The string contains extra characters after the integer.");
+  }
+  // highlight-end
+  return result;
+}
+
+int main() {
+  std::string str = "123";
+  int value = stringToInteger(str);
+  std::cout << "The value is: " << value << std::endl;
+}
+```
+<codapi-snippet sandbox="cpp" editor="basic" init-delay="500">
+</codapi-snippet>
+
+In the preceding code, the program first tries to extract an integer from the string. If the stream state is `fail` or `bad`, it throws an error. Otherwise, it tries to extract a character from the remaining string. If the stream state is not `fail`, it means that the string contains extra characters after the integer. Then, the program throws an error.
+
+Since `if ((iss >> result).fail())` is equivalent to `if (!(iss >> result))`, we can simplify the code as follows:
+
+```cpp name="stringToInteger.cpp"
+#include <iostream>
+#include <sstream>
+
+int stringToInteger(const std::string &str) {
+  std::istringstream iss(str);
+  int result;
+  char remain;  // Record remaining characters after the integer
+  // highlight-start
+  if (!(iss >> result) || iss >> remain) {
+    throw std::domain_error(
+        "Failed to get integer from string. Please check the string.");
+  }
+  // highlight-end
+  return result;
+}
+
+int main() {
+  std::string str = "123";
+  int value = stringToInteger(str);
+  std::cout << "The value is: " << value << std::endl;
+}
+```
+<codapi-snippet sandbox="cpp" editor="basic" init-delay="500">
+</codapi-snippet>
diff --git a/website/docs/cpp/cpp-wiki.md b/website/docs/cpp/cpp-wiki.md
index a25a37a..8099742 100644
--- a/website/docs/cpp/cpp-wiki.md
+++ b/website/docs/cpp/cpp-wiki.md
@@ -1,5 +1,5 @@
 ---
-title: "C++"
+title: "C++ wiki"
 description: "A collection of useful C++ usage and tips."
 ---
 
@@ -20,7 +20,7 @@ using namespace std;
 
 int max = 0;
 int main() {
-    cout << max << endl; // error: reference to 'max' is ambiguous
+  cout << max << endl;  // error: reference to 'max' is ambiguous
 }
 ```
 
@@ -34,7 +34,7 @@ To avoid the preceding error, use the following code instead:
 
 int max = 0;
 int main() {
-    std::cout << max << std::endl; // 0
+  std::cout << max << std::endl;  // 0
 }
 ```
 
@@ -54,11 +54,11 @@ The following code examples show the difference between using `std::endl` and no
 
   ```cpp
   #include <iostream>
-
+  
   int main() {
-      for (int i=0; i<5; i++) {
-          std::cout << i << std::endl;
-      }
+    for (int i = 0; i < 5; i++) {
+      std::cout << i << std::endl;
+    }
   }
   // 0
   // 1
@@ -74,11 +74,11 @@ The following code examples show the difference between using `std::endl` and no
 
   ```cpp
   #include <iostream>
-
+  
   int main() {
-      for (int i=0; i<5; i++) {
-          std::cout << i; // 01234
-      }
+    for (int i = 0; i < 5; i++) {
+      std::cout << i;  // 01234
+    }
   }
   ```
   <codapi-snippet sandbox="cpp" editor="basic" init-delay="500">
@@ -106,14 +106,15 @@ The following code examples show the same output with `std::endl` and `\n` in st
   <TabItem label="Use std::endl in standard output" value="std_endl_std_out">
 
   ```cpp name="std_endl.cpp"
-  #include <iostream>
   #include <unistd.h>
-
+  
+  #include <iostream>
+  
   int main() {
-      for (int i=0; i<5; i++) {
-          sleep(1);
-          std::cout << i << std::endl;
-      }
+    for (int i = 0; i < 5; i++) {
+      sleep(1);
+      std::cout << i << std::endl;
+    }
   }
   // Sleep 1 second
   // 0
@@ -131,14 +132,15 @@ The following code examples show the same output with `std::endl` and `\n` in st
   <TabItem label="Use new line character in standard output" value="new_line_std_out">
 
   ```cpp name="new_line_character.cpp"
-  #include <iostream>
   #include <unistd.h>
-
+  
+  #include <iostream>
+  
   int main() {
-      for (int i=0; i<5; i++) {
-          sleep(1);
-          std::cout << i << "\n";
-      }
+    for (int i = 0; i < 5; i++) {
+      sleep(1);
+      std::cout << i << "\n";
+    }
   }
   // Sleep 1 second
   // 0
@@ -200,35 +202,40 @@ The following example shows the duration for printing 100,000 numbers with `std:
   <TabItem label="Code" value="code">
 
   ```cpp
-  #include <iostream> // for cin, cout
-  #include <chrono> // for timers
+  #include <chrono>    // for timers
+  #include <iostream>  // for cin, cout
   
   int endl_each_time(int n = 10000) {
-      const auto start_time = std::chrono::high_resolution_clock::now();
-      for (int i = 0; i < n; i++) {
-          std::cout << i << std::endl;
-      }
-      const auto end_time = std::chrono::high_resolution_clock::now();
-      auto duration_ns = std::chrono::duration_cast<std::chrono::microseconds>(end_time - start_time);
-      return duration_ns.count();
+    const auto start_time = std::chrono::steady_clock::now();
+    for (int i = 0; i < n; i++) {
+      std::cout << i << std::endl;
+    }
+    const auto end_time = std::chrono::steady_clock::now();
+    auto duration_ns = std::chrono::duration_cast<std::chrono::microseconds>(
+        end_time - start_time);
+    return duration_ns.count();
   }
   
   int new_line_each_time(int n = 10000) {
-      const auto start_time = std::chrono::high_resolution_clock::now();
-      for (int i = 0; i < n; i++) {
-          std::cout << i << "\n";
-      }
-      const auto end_time = std::chrono::high_resolution_clock::now();
-      const auto duration_ns = std::chrono::duration_cast<std::chrono::microseconds>(end_time - start_time);
-      return duration_ns.count();
+    const auto start_time = std::chrono::steady_clock::now();
+    for (int i = 0; i < n; i++) {
+      std::cout << i << "\n";
+    }
+    const auto end_time = std::chrono::steady_clock::now();
+    const auto duration_ns =
+        std::chrono::duration_cast<std::chrono::microseconds>(end_time -
+                                                              start_time);
+    return duration_ns.count();
   }
   
   int main() {
-      int endl_duration = endl_each_time();
-      int new_line_duration = new_line_each_time();
-      std::cout << "endl_each_time duration: " << endl_duration << "ns" << std::endl;
-      std::cout << "new_line_each_time duration: " << new_line_duration << "ns" << std::endl;
-      return 0;
+    int endl_duration = endl_each_time();
+    int new_line_duration = new_line_each_time();
+    std::cout << "endl_each_time duration: " << endl_duration << "ns"
+              << std::endl;
+    std::cout << "new_line_each_time duration: " << new_line_duration << "ns"
+              << std::endl;
+    return 0;
   }
   ```
 
@@ -238,8 +245,8 @@ The following example shows the duration for printing 100,000 numbers with `std:
   ```shell
   ...
   9999
-  endl_each_time duration: 9717ns
-  new_line_each_time duration: 8896ns
+  endl_each_time duration: 15699ns
+  new_line_each_time duration: 10613ns
   ```
 
   </TabItem>
diff --git a/website/docs/cpp/guess-number.md b/website/docs/cpp/guess-number.md
new file mode 100644
index 0000000..ed67be1
--- /dev/null
+++ b/website/docs/cpp/guess-number.md
@@ -0,0 +1,542 @@
+---
+title: "Building a Guess Number Game"
+---
+
+```mdx-code-block
+import Tabs from '@theme/Tabs';
+import TabItem from '@theme/TabItem';
+```
+
+这篇博客记录了我跟着 [C++ Beginner's Guide](https://hackingcpp.com/cpp/beginners_guide.html) 学习 C++ 的第一天，并通过一个猜数字游戏的实践来加深对 I/O、基本数据类型、控制流等基础知识的理解。
+
+## 准备开发环境
+
+在 macOS 上，可以直接使用 clang/clang++ 来编译 C++ 代码，也可以使用 gcc/g++ 命令，因为他们指向的均为 clang：
+
+```bash
+# highlight-next-line
+> gcc --version
+Apple clang version 14.0.0 (clang-1400.0.29.202)
+Target: arm64-apple-darwin22.3.0
+Thread model: posix
+InstalledDir: /Library/Developer/CommandLineTools/usr/bin
+# highlight-next-line
+> g++ --version
+Apple clang version 14.0.0 (clang-1400.0.29.202)
+Target: arm64-apple-darwin22.3.0
+Thread model: posix
+InstalledDir: /Library/Developer/CommandLineTools/usr/bin
+# highlight-next-line
+> clang --version
+Apple clang version 14.0.0 (clang-1400.0.29.202)
+Target: arm64-apple-darwin22.3.0
+Thread model: posix
+InstalledDir: /Library/Developer/CommandLineTools/usr/bin
+# highlight-next-line
+> clang++ --version
+Apple clang version 14.0.0 (clang-1400.0.29.202)
+Target: arm64-apple-darwin22.3.0
+Thread model: posix
+InstalledDir: /Library/Developer/CommandLineTools/usr/bin
+```
+
+你也可以使用 [`cpp.sh`](https://cpp.sh) 在线运行 C++ 代码。其它平台的安装方式可以参考 [C++ Development Setup](https://hackingcpp.com/cpp/tools/beginner_dev_setup.html)。
+
+## 学习基础知识
+
+首先，参考 [Hello World](https://hackingcpp.com/cpp/hello_world.html) 学习如何编写、编译并运行一个简单的 C++ 程序。
+
+1. 创建一个名为 `hello.cpp` 的文件，内容如下：
+
+  ```cpp title="hello.cpp"
+  #include <iostream>
+  int main()
+  {
+      std::cout << "Hello World!\n";
+  }
+  ```
+
+2. 将 `hello.cpp` 编译为可执行文件 `hello` 并运行：
+
+  ```bash
+  g++ hello.cpp -o hello && ./hello
+
+  # Hello World!
+  ```
+
+第一个简单的 `hello.cpp` 程序主要包含了以下几个部分：
+
+- `#include <iostream>`：包含了 C++ 标准库中的 `iostream` 头文件，该头文件包含了 `std::cout` 和 `std::cin` 等用于输入输出的对象。
+- `int main()`：程序的入口函数，所有的 C++ 程序都必须包含一个 `main` 函数。
+- `std::cout << "Hello World!\n";`：输出字符串 `"Hello World!"`，并在末尾添加一个换行符 `\n`。
+
+### 输入与输出
+
+C++ 中的输入输出可以通过 [`std::cin`](https://en.cppreference.com/w/cpp/io/cin) 和 [`std::cout`](https://en.cppreference.com/w/cpp/io/cout) 对象来实现：
+
+- `std::cin`：用于从标准输入（通常是键盘）读取数据。
+- `std::cout`：用于向标准输出（通常是屏幕）输出数据。
+
+下面是一个使用 `std::cin` 和 `std::cout` 的简单示例：
+
+```cpp title="io.cpp"
+#include <iostream>
+
+int main() {
+  int a, b;
+  std::cout << "Enter two numbers: ";
+  std::cin >> a >> b;
+  std::cout << "The numbers you entered are: " << a << " and " << b << '\n';
+}
+```
+
+将 `io.cpp` 编译为可执行文件 `a.out`（未指定 `-o` 时的默认值）并运行：
+
+```bash
+g++ --std=c++20 io.cpp && ./a.out
+
+# Enter two numbers: 2 3
+# The numbers you entered are: 2 and 3
+```
+
+在上面的示例程序中：
+
+- 输入时使用了 `std::cin >> a >> b;` 语句读取两个数值并分别赋值给 `a` 和 `b`。
+- 输出时使用了 `std::cout << "The numbers you entered are: " << a << " and " << b << '\n';` 语句将 `a` 和 `b` 的值输出到屏幕上。
+- `>>` 和 `<<` 为流操作符，用于将数据从流中读取或写入到流中。
+
+更多信息可以参考 [Input & Output (Basics)](https://hackingcpp.com/cpp/std/io_basics.html)。
+
+### 变量声明与数据类型
+
+C++ 中声明变量的语法为：
+
+```cpp
+type variable = value;
+```
+
+例如，声明一个整型变量 `a` 并赋值为 `5`：
+
+```cpp
+int a = 5;
+```
+
+更多信息可以参考 [Fundamental Types](https://hackingcpp.com/cpp/lang/fundamental_types.html)。
+
+### 控制流
+
+关于控制流的详细信息可以参考 [Control Flow (Basics)](https://hackingcpp.com/cpp/lang/control_flow_basics.html)。
+
+#### 条件
+
+条件语句可以通过 `if`、`else` 和 `else if` 关键字来实现，语法如下：
+
+```cpp
+if (condition1) {
+  // do this if condition1 is true
+} else if (condition2) {
+  // else this id condition2 is true
+} else {
+  // otherwise do this
+}
+```
+
+下面是判断输入的数字是正数、负数还是零的示例程序：
+
+```cpp title="condition.cpp"
+#include <iostream>
+
+int main() {
+  int i = 0;
+  std::cout << "Enter a number: ";
+  std::cin >> i;
+  if (i == 0) {
+    std::cout << "zero\n";
+  } else if (i > 0) {
+    std::cout << "positive\n";
+  } else {
+    std::cout << "negative\n";
+  }
+}
+```
+
+将 `condition.cpp` 编译为可执行文件并运行：
+
+```bash
+g++ --std=c++20 condition.cpp && ./a.out
+
+#Enter a number: 0
+# zero
+
+# Enter a number: 1
+# positive
+
+# Enter a number: -1
+# negative
+```
+
+### 循环
+
+C++ 中的循环语句可以通过 `while`、`do while` 和 `for` 关键字来实现，使用示例如下：
+
+### `while`
+
+下面示例输出结果为 `5 6 7 8 9`：
+
+```cpp title="while.cpp"
+#include <iostream>
+
+int main() {
+  int i = 5;
+  while (i < 10) {
+    std::cout << i << ' ';
+    i = i + 1;
+  }
+}
+```
+<codapi-snippet sandbox="cpp" init-delay="500">
+</codapi-snippet>
+
+### `do ... while`
+
+下面示例输出结果为 `10`：
+
+```cpp title="do_while.cpp"
+#include <iostream>
+
+int main() {
+  int i = 10;
+  do {
+    std::cout << i << ' ';
+    i = i + 1;
+  } while (i < 10);
+}
+```
+<codapi-snippet sandbox="cpp" init-delay="500">
+</codapi-snippet>
+
+#### `for`
+
+下面示例输出结果为 `5 6 7 8 9`：
+
+```cpp title="for.cpp"
+#include <iostream>
+
+int main() {
+  for (int i = 5; i < 10; i = i + 1) {
+    std::cout << i << ' ';
+  }
+}
+```
+<codapi-snippet sandbox="cpp" init-delay="500">
+</codapi-snippet>
+
+
+## 实践：猜数字游戏
+
+编写一个猜数字游戏，程序随机生成一个 1 到 100 之间的整数，用户输入一个数字，程序判断用户输入的数字是否正确，如果错误则提示用户输入的数字过大或过小，直到用户猜中为止。
+
+### 伪代码
+
+```
+1. 生成一个 1 到 100 之间的随机数
+2. 用户输入一个数字 guess_number
+3. 如果 guess_number == random_number，则提示用户猜中，游戏结束
+4. 如果 guess_number > random_number，则提示用户输入的数字过大，然后跳转到第 2 步
+5. 如果 guess_number < random_number，则提示用户输入的数字过小，然后跳转到第 2 步
+```
+
+### 生成随机数
+
+首先需要解决的问题是如何生成一个 1 到 100 之间的随机数。可以在 [cppreference.com](https://en.cppreference.com/w/cpp/io/cin) 中搜索 `rand`，找到 [`std::rand`](https://en.cppreference.com/w/cpp/numeric/random/rand) 函数。该函数用于生成一个 `[0, RAND_MAX]` 之间的随机数，并不符合我们的需求。但是，在 [`std::rand`](https://en.cppreference.com/w/cpp/numeric/random/rand) 文档的 See also 章节可以看到：
+
+:::info quote
+
+- uniform_int_distribution: produces **integer** values **evenly** distributed **across a range**
+- srand: seeds pseudo-random number generator
+- RAND_MAX: maximum possible value generated by `std::rand`
+- randint: generates a **random integer in the specified range**
+
+:::
+
+因此可以使用 [`std::uniform_int_distribution`](https://en.cppreference.com/w/cpp/numeric/random/uniform_int_distribution) 生成一个 `[min, max]` 之间的随机数。
+
+```cpp title="guess_number.cpp"
+#include <iostream>
+// highlight-next-line
+#include <random>
+
+int main() {
+  std::random_device rd;
+  std::mt19937 gen(rd());
+  std::uniform_int_distribution<> distrib(1, 100);
+  int answer = distrib(gen);
+
+  std::cout << "The answer is: " << answer;
+}
+```
+<codapi-snippet sandbox="cpp" init-delay="500">
+</codapi-snippet>
+
+### 处理用户输入
+
+用户输入的数字可以通过 `std::cin` 来获取：
+
+```cpp title="guess_number.cpp"
+#include <iostream>
+#include <random>
+
+int main() {
+  std::random_device rd;
+  std::mt19937 gen(rd());
+  std::uniform_int_distribution<> distrib(1, 100);
+  int answer = distrib(gen);
+
+  std::cout << "The answer is: " << answer << '\n';
+
+  // highlight-start
+  int guess_number;
+  std::cout << "Guess the number: ";
+  std::cin >> guess_number;
+  // highlight-end
+
+  std::cout << "The guess_number is: " << guess_number << '\n';
+}
+```
+<codapi-snippet sandbox="cpp" init-delay="500">
+</codapi-snippet>
+
+### 判断用户输入的数字是否正确
+
+使用 `if` 语句来判断用户输入的数字是否正确：
+
+```cpp title="guess_number.cpp"
+#include <iostream>
+#include <random>
+
+int main() {
+  std::random_device rd;
+  std::mt19937 gen(rd());
+  std::uniform_int_distribution<> distrib(1, 100);
+  int answer = distrib(gen);
+
+  std::cout << "The answer is: " << answer << '\n';
+
+  int guess_number;
+  std::cout << "Guess the number: ";
+  std::cin >> guess_number;
+
+  std::cout << "The guess_number is: " << guess_number << '\n';
+
+  // highlight-start
+  if (guess_number == answer) {
+    std::cout << "Congratulations!\n";
+  } else if (guess_number < answer) {
+    std::cout << "Guess a higher number!\n";
+  } else {
+    std::cout << "Guess a lower number!\n";
+  }
+  // highlight-end
+}
+```
+
+### 添加循环
+
+使用 `while` 循环在用户没有猜中的情况下一直提示用户输入：
+
+```cpp title="guess_number.cpp"
+#include <iostream>
+#include <random>
+
+int main() {
+  std::random_device rd;
+  std::mt19937 gen(rd());
+  std::uniform_int_distribution<> distrib(1, 100);
+  int answer = distrib(gen);
+
+  std::cout << "The answer is: " << answer << '\n';
+
+  // highlight-next-line
+  while (true) {
+    int guess_number;
+    std::cout << "Guess the number: ";
+    std::cin >> guess_number;
+
+    if (guess_number == answer) {
+      std::cout << "Congratulations!\n";
+      // highlight-next-line
+      break;
+    } else if (guess_number < answer) {
+      std::cout << "Guess a higher number!\n";
+    } else {
+      std::cout << "Guess a lower number!\n";
+    }
+  }
+}
+```
+
+使用示例如下：
+
+```bash
+g++ --std=c++20 guess_number.cpp && ./a.out
+# The answer is: 5
+# Guess the number: 2
+# Guess a higher number!
+# Guess the number: 4
+# Guess a higher number!
+# Guess the number: 5
+# Congratulations!
+```
+
+### 提供当前猜数字的范围
+
+在提示用户输入更大或更小数值时，可以提供更准确的正确数字范围。在程序处理中，需要在 `while` 循环内记录并维护当前的数字范围：
+
+- 当 `guess_number < answer` 时，`min_val` 应该更新为 `guess_number + 1`，`max_val` 不变。
+- 当 `guess_number > answer` 时，`min_val` 不变，`max_val` 应该更新为 `guess_number - 1`。
+
+```cpp title="guess_number.cpp"
+#include <iostream>
+#include <random>
+
+int main() {
+  // highlight-start
+  int min_val = 1;
+  int max_val = 100;
+  // highlight-end
+  std::random_device rd;
+  std::mt19937 gen(rd());
+  // highlight-next-line
+  std::uniform_int_distribution<> distrib(min_val, max_val);
+  int answer = distrib(gen);
+
+  std::cout << "The answer is: " << answer << '\n';
+
+  while (true) {
+    int guess_number;
+    std::cout << "Guess the number: ";
+    std::cin >> guess_number;
+
+    if (guess_number == answer) {
+      std::cout << "Congratulations!\n";
+      break;
+    } else if (guess_number < answer) {
+      // highlight-start
+      min_val = guess_number + 1;
+      std::cout << "Guess the number from " << min_val << " to " << max_val
+                << '\n';
+      // highlight-end
+    } else {
+      // highlight-start
+      max_val = guess_number - 1;
+      std::cout << "Guess the number from " << min_val << " to " << max_val
+                << '\n';
+      // highlight-end
+    }
+  }
+}
+```
+
+在测试时发现，如果猜测的数字不在当前范围内，程序给出的提示信息不准确。例如，如果当前范围为 `[56, 69]`，而用户输入的数字为 `52`，此时程序提示的范围为 `[53, 69]`，这是不正确的。
+
+```bash
+g++ --std=c++20 guess_number.cpp && ./a.out
+# The answer is: 57
+# Guess the number: 50
+# Guess the number from 51 to 100
+# Guess the number: 70
+# Guess the number from 51 to 69
+# Guess the number: 55
+# Guess the number from 56 to 69
+# Guess the number: 52
+# Guess the number from 53 to 69
+```
+
+为了解决这个问题，需要在更改 `min_val` 或 `max_val` 时，判断取值是否在当前范围内：
+
+```cpp title="guess_number.cpp"
+#include <iostream>
+#include <random>
+
+int main() {
+  int min_val = 1;
+  int max_val = 100;
+  std::random_device rd;
+  std::mt19937 gen(rd());
+  std::uniform_int_distribution<> distrib(min_val, max_val);
+  int answer = distrib(gen);
+
+  std::cout << "The answer is: " << answer << '\n';
+
+  while (true) {
+    int guess_number;
+    std::cout << "Guess the number: ";
+    std::cin >> guess_number;
+
+    if (guess_number == answer) {
+      std::cout << "Congratulations!\n";
+      break;
+    } else if (guess_number < answer) {
+      // highlight-next-line
+      min_val = guess_number < min_val ? min_val : guess_number + 1;
+      std::cout << "Guess the number from " << min_val << " to " << max_val
+                << '\n';
+    } else {
+      // highlight-next-line
+      max_val = guess_number > max_val ? max_val : guess_number - 1;
+      std::cout << "Guess the number from " << min_val << " to " << max_val
+                << '\n';
+    }
+  }
+}
+```
+
+修改后的程序输出如下：
+
+```bash
+g++ --std=c++20 guess_number.cpp && ./a.out
+# The answer is: 57
+# Guess the number: 50
+# Guess the number from 51 to 100
+# Guess the number: 70
+# Guess the number from 51 to 69
+# Guess the number: 55
+# Guess the number from 56 to 69
+# Guess the number: 52
+# Guess the number from 56 to 69
+```
+
+### 整体代码
+
+```cpp title="guess_number.cpp"
+#include <iostream>
+#include <random>
+
+int main() {
+  int min_val = 1;
+  int max_val = 100;
+  std::random_device rd;
+  std::mt19937 gen(rd());
+  std::uniform_int_distribution<> distrib(min_val, max_val);
+  int answer = distrib(gen);
+
+  while (true) {
+    int guess_number;
+    std::cout << "Guess the number: ";
+    std::cin >> guess_number;
+
+    if (guess_number == answer) {
+      std::cout << "Congratulations!\n";
+      break;
+    } else if (guess_number < answer) {
+      min_val = guess_number < min_val ? min_val : guess_number + 1;
+      std::cout << "Guess the number from " << min_val << " to " << max_val
+                << '\n';
+    } else {
+      max_val = guess_number > max_val ? max_val : guess_number - 1;
+      std::cout << "Guess the number from " << min_val << " to " << max_val
+                << '\n';
+    }
+  }
+}
+```
diff --git a/website/docs/cpp/stringtoint-stringstream.md b/website/docs/cpp/stringtoint-stringstream.md
new file mode 100644
index 0000000..e35029c
--- /dev/null
+++ b/website/docs/cpp/stringtoint-stringstream.md
@@ -0,0 +1,302 @@
+---
+title: "Get an Integer from a String Using string stream"
+description: "During the CS 106L course, I learned a lot of C++ streams. This document describes how to use basic_stringstream to get an integer from a string."
+---
+
+```mdx-code-block
+import Tabs from '@theme/Tabs';
+import TabItem from '@theme/TabItem';
+```
+
+During the CS 106L course, I learned a lot of C++ streams. This document describes how to use [`basic_stringstream`](https://en.cppreference.com/w/cpp/io/basic_stringstream) to get an integer from a string.
+
+:::info quote
+
+The basic unit of communication between a program and its environment is a _stream_. A stream is a channel between a _source_ and _destination_ which allows the source to push formatted data to the destination.
+
+—— [CS 106L Course Reader](https://web.stanford.edu/class/cs106l/full_course_reader.pdf)
+
+:::
+
+## Overview of string stream
+
+To create a string stream, we need to include the `<sstream>` header file. Then, we can create a string stream object using the following code:
+
+```cpp
+#include <sstream>
+
+int main() {
+  std::istringstream iss("9.15 pounds.");
+  std::ostringstream oss("The price of the shirt is ");
+}
+```
+
+For C++ beginners, we usually use `std::cin` to get input from the user and use `std::cout` to output something to the console. Here, `std::cin` and `std::cout` are both streams. The following is an example:
+
+```cpp
+#include <iostream>
+
+int main() {
+  int value;
+  std::cin >> value;
+  std::cout << value << std::endl;
+}
+```
+
+In the preceding example, `>>` is the stream **extraction** operator, and `<<` is the stream **insertion** operator. For string streams, we also use `>>` and `<<` to extract and insert data.
+
+To extract the price and unit from the string stream `iss`, use the following code:
+
+<Tabs>
+  <TabItem value="extract-price-double-code" label="Extract price (double) and unit">
+  
+  ```cpp
+  #include <iostream>
+  #include <sstream>
+  
+  int main() {
+    std::istringstream iss("9.15 pounds.");
+    std::ostringstream oss("The price of the shirt is ");
+    double price;
+    std::string unit;
+    iss >> price >> unit;
+    std::cout << oss.str() << price << " " << unit << std::endl;
+  }
+  ```
+  <codapi-snippet sandbox="cpp" init-delay="500">
+  </codapi-snippet>
+
+  </TabItem>
+  <TabItem value="extract-price-double-output" label="Output">
+  
+  ```text
+  The price of the shirt is 9.15 pounds.
+  ```
+
+  </TabItem>
+</Tabs>
+
+What is the behavior of `iss >> price >> unit`? We can modify the type of `price` to `int` and see what happens:
+
+<Tabs>
+  <TabItem value="extract-price-int-code" label="Extract price (int) and unit">
+  
+  ```cpp
+  #include <iostream>
+  #include <sstream>
+  
+  int main() {
+    std::istringstream iss("9.15 pounds.");
+    std::ostringstream oss("The price of the shirt is ");
+    // highlight-next-line
+    int price;
+    std::string unit;
+    iss >> price >> unit;
+    std::cout << oss.str() << price << " " << unit << std::endl;
+  }
+  ```
+  <codapi-snippet sandbox="cpp" init-delay="500">
+  </codapi-snippet>
+
+  </TabItem>
+  <TabItem value="extract-price-int-output" label="Output">
+  
+  ```text
+  The price of the shirt is 9 .15
+  ```
+
+  </TabItem>
+</Tabs>
+
+The output shows that the value of `price` is `9`, and the value of `unit` is `.15`. This is because the `>>` operator will stop extracting data when it encounters a whitespace or an invalid character for the type. In this case, the `>>` operator in `iss >> price` stops extracting data at `.`. Then, the `>>` operator in `iss >> unit` extracts `.15` into `unit` and stops extracting data at ` `.
+
+## Implement `stringToInteger()` without error-checking
+
+Now, we can use `>>` to extract an integer from a string. Let's implement a function `stringToInteger()` to convert a string to an integer. The code is as follows:
+
+<Tabs>
+  <TabItem value="string-to-int-first" label="Extract an integer from a string">
+  
+  ```cpp name="stringToInteger.cpp"
+  #include <iostream>
+  #include <sstream>
+  
+  int stringToInteger(const std::string& str) {
+    std::istringstream iss(str);
+    int value;
+    iss >> value;
+    return value;
+  }
+  
+  int main() {
+    std::string str = "123";
+    int value = stringToInteger(str);
+    std::cout << "The value is: " << value << std::endl;
+  }
+  ```
+  <codapi-snippet sandbox="cpp" init-delay="500">
+  </codapi-snippet>
+
+  </TabItem>
+  <TabItem value="string-to-int-first-output" label="Output">
+  
+  ```text
+  The value is: 123
+  ```
+
+  </TabItem>
+</Tabs>
+
+## Stream state
+
+What if the string contains invalid characters? For example, the string `"123abc"` contains non-numeric characters. In this case, the `>>` operator stops extracting data at `a`. Then, the value of `value` will be `123`. However, we want to return an error message to the user. To do this, we need to check whether any error occurs during the extraction process.
+
+A new concept is introduced here: **stream state**. There are four stream states:
+
+- **good**: no error occurs. The I/O operations are available.
+- **eof**: reaching the **end of the stream**.
+- **fail**: the input/output operation failed and all future operations frozen, such as the type mismatch.
+- **bad**: **irrecoverable** stream error. For example, the file you are reading is deleted suddenly.
+
+To check the stream state, we can use the `good()`, `eof()`, `fail()`, and `bad()` functions. The following shows some examples:
+
+<Tabs>
+  <TabItem value="stream-state-code" label="Check stream state">
+  
+  ```cpp
+  #include <iostream>
+  #include <sstream>
+  #include <vector>
+  
+  void get_stream_state(std::istringstream &iss) {
+    if (iss.good()) {
+      std::cout << "G";
+    }
+    if (iss.eof()) {
+      std::cout << "E";
+    }
+    if (iss.fail()) {
+      std::cout << "F";
+    }
+    if (iss.bad()) {
+      std::cout << "B";
+    }
+    std::cout << std::endl;
+  }
+  
+  int stringToInteger(const std::string &str) {
+    std::istringstream iss(str);
+    std::cout << "Before: ";
+    get_stream_state(iss);
+    int value;
+    iss >> value;
+    std::cout << "After: ";
+    get_stream_state(iss);
+    return value;
+  }
+  
+  int main() {
+    std::vector<std::string> test_strings{"123", "123abc", "abc123", ""};
+    for (const auto &str : test_strings) {
+      std::cout << "stringToInteger(\"" << str << "\"):\n"
+                << stringToInteger(str) << std::endl;
+    }
+  }
+  ```
+  <codapi-snippet sandbox="cpp" init-delay="500">
+  </codapi-snippet>
+
+  </TabItem>
+  <TabItem value="stream-state-output" label="Output">
+  
+  ```text
+  stringToInteger("123"):
+  Before: G
+  After: E
+  123
+  stringToInteger("123abc"):
+  Before: G
+  After: G
+  123
+  stringToInteger("abc123"):
+  Before: G
+  After: F
+  0 # undefined behavior
+  stringToInteger(""):
+  Before: G
+  After: EF
+  -514166240 # undefined behavior
+  ```
+
+  </TabItem>
+</Tabs>
+
+## Implement `stringToInteger()` with error-checking
+
+Using the stream state, we can implement `stringToInteger()` with error-checking. From the preceding example, to ensure that the string only contains numeric characters, we need to consider the following cases:
+
+- After the extraction, the stream state is `good` : the string might contain non-numeric characters after the number.
+- After the extraction, the stream state is `fail`: the string contains non-numeric characters before the number.
+
+The following code shows how to implement `stringToInteger()` with error-checking:
+
+```cpp name="stringToInteger.cpp"
+#include <iostream>
+#include <sstream>
+
+int stringToInteger(const std::string &str) {
+  std::istringstream iss(str);
+  int result;
+  // highlight-start
+  char remain;  // Record remaining characters after the integer
+  iss >> result;
+  if (iss.fail() || iss.bad()) {
+    throw std::domain_error("The string does not start with an integer.");
+  }
+  iss >> remain;
+  if (!iss.fail()) {
+    throw std::domain_error(
+        "The string contains extra characters after the integer.");
+  }
+  // highlight-end
+  return result;
+}
+
+int main() {
+  std::string str = "123";
+  int value = stringToInteger(str);
+  std::cout << "The value is: " << value << std::endl;
+}
+```
+<codapi-snippet sandbox="cpp" editor="basic" init-delay="500">
+</codapi-snippet>
+
+In the preceding code, the program first tries to extract an integer from the string. If the stream state is `fail` or `bad`, it throws an error. Otherwise, it tries to extract a character from the remaining string. If the stream state is not `fail`, it means that the string contains extra characters after the integer. Then, the program throws an error.
+
+Since `if ((iss >> result).fail())` is equivalent to `if (!(iss >> result))`, we can simplify the code as follows:
+
+```cpp name="stringToInteger.cpp"
+#include <iostream>
+#include <sstream>
+
+int stringToInteger(const std::string &str) {
+  std::istringstream iss(str);
+  int result;
+  char remain;  // Record remaining characters after the integer
+  // highlight-start
+  if (!(iss >> result) || iss >> remain) {
+    throw std::domain_error(
+        "Failed to get integer from string. Please check the string.");
+  }
+  // highlight-end
+  return result;
+}
+
+int main() {
+  std::string str = "123";
+  int value = stringToInteger(str);
+  std::cout << "The value is: " << value << std::endl;
+}
+```
+<codapi-snippet sandbox="cpp" editor="basic" init-delay="500">
+</codapi-snippet>