diff --git a/cxx-parser/__tests__/unit_test/cxx_terra_node_ext.test.ts b/cxx-parser/__tests__/unit_test/cxx_terra_node_ext.test.ts
new file mode 100644
index 0000000..3beae67
--- /dev/null
+++ b/cxx-parser/__tests__/unit_test/cxx_terra_node_ext.test.ts
@@ -0,0 +1,17 @@
+import fs from 'fs';
+import os from 'os';
+import path from 'path';
+
+import '../../src/cxx_terra_node_ext';
+import { SimpleType, SimpleTypeKind } from '../../src/cxx_terra_node';
+
+describe('cxx_terra_node_ext', () => {
+  it('lenOfArrayType can get len of array type', () => {
+    let simpleType = new SimpleType();
+    simpleType.kind = SimpleTypeKind.array_t;
+    simpleType.source = 'int[10]';
+
+    let len = simpleType.lenOfArrayType();
+    expect(len).toBe('10');
+  });
+});
diff --git a/cxx-parser/src/cxx_terra_node_ext.ts b/cxx-parser/src/cxx_terra_node_ext.ts
index f11c927..98161c3 100644
--- a/cxx-parser/src/cxx_terra_node_ext.ts
+++ b/cxx-parser/src/cxx_terra_node_ext.ts
@@ -1,3 +1,7 @@
+import { strict as assert } from 'assert';
+
+import { SimpleType, SimpleTypeKind } from './cxx_terra_node';
+
 export {};
 
 declare global {
@@ -17,6 +21,15 @@ declare global {
   }
 }
 
+declare module '@agoraio-extensions/cxx-parser' {
+  export interface SimpleType {
+    /**
+     * The length of the array type. For example, "int[10]" returns "10".
+     */
+    lenOfArrayType(): string;
+  }
+}
+
 /**
  * This function removes the namespace from a fully qualified name.
  * For example, "foo::bar" becomes "bar".
@@ -51,3 +64,19 @@ String.prototype.getNamespace = function (): string {
   const splitted = this.split('::');
   return Array.from(splitted.slice(0, splitted.length - 1)).join('::');
 };
+
+/**
+ * The length of the array type. For example, "int[10]" returns "10".
+ */
+SimpleType.prototype.lenOfArrayType = function (): string {
+  assert(this.kind === SimpleTypeKind.array_t);
+  assert(this.source);
+
+  let regex = new RegExp(/\d+/);
+  let len = this.source.match(regex);
+  if (len) {
+    return len[0];
+  }
+
+  assert(false); // Should not reach here
+};
diff --git a/cxx-parser/src/index.ts b/cxx-parser/src/index.ts
index 49d81e5..e8822ff 100644
--- a/cxx-parser/src/index.ts
+++ b/cxx-parser/src/index.ts
@@ -1,5 +1,7 @@
-export * from './cxx_terra_node';
+// This should be above the `cxx_terra_node`, or it will throw TypeError: Cannot read properties of undefined (reading 'xxx')
 export * from './cxx_terra_node_ext';
+export * from './cxx_terra_node';
 export * from './cxx_parser_configs';
-export * from './cxx_parser';
+// This should be above the `cxx_parser`, or it will throw TypeError: Cannot read properties of undefined (reading 'xxx')
 export * from './cxx_parser_ext';
+export * from './cxx_parser';