README.md

PCPP — The Pre-C Preprocessor

The Pre-C Preprocessor is a lightweight tool designed to partially preprocess C code. This tool is intended to simplify C code that is littered with large amounts of derictives.

Behaviour

Like coan, pcpp treats any macro that has not been explicitly defined or undefined as UNDETERMINED. This mostly affects conditionals. If a conditional has any undetermined macros, the conditional is not processed, but the contents of all the branches are processed. Therefore, a define directive inside an undetermined conditional will be resolved, which might lead to undesired behavior. To turn off this behavior, use --ignore-undetermined. As an example:

#ifdef SOME_MACRO
#	define OTHER_MACRO
#endif

Running pcpp --define-all input leads to:

#ifdef SOME_MACRO
#endif

If you are abusing backslash-newline in your directives, then the behaviour of pcpp is not clear. It can either be added to the final code as is, or it might cause the parser to crash. the following example shows both:

// The following is parsed correctly
#define test do {   \
	printf("test"); \
} while (0);

// The following line crashes the parser
#ifdef macro \

#endif

Building

1. Bootstrap build system: cc -o nobuild nobuild.c
2. Run build system: ./nobuild

Examples

The file string.h:

#ifndef string_h
#define string_h

#ifdef MACRO
void macro_func();
#elifdef
void macro_func_undef();
#endif

void void_func();

#endif  // string_h

#ifdef string_implementation
#ifndef string_i
#define string_i

void void_func() {
}

#endif  // string_i
#endif  // string_implementation

The file main.c:

#define MACRO
#include "string.h"

#ifdef X
#	ifndef MACRO
		do_thing();
#	endif
#	ifdef Y
		do_thing_with_Y_and_X();
#	endif
#elifdef Y
#	ifndef Z
#		define Z
		do_thing_with_Y_and_Z();
#	endif
#elifndef Z
	do_setup();
#else
	crash();
#endif

#define string_implementation
#include "string.h"

Commands:

1. pcpp --implicitly-undef --only=string_h,string_i,string_implementation --include-all main.c:

   #define MACRO
   
   #ifdef MACRO
   void macro_func();
   #elifdef
   void macro_func_undef();
   #endif
   
   void void_func();
   
   
   
   int main(void)
   {
   #ifdef X
   #	ifndef MACRO
   		do_thing();
   #	endif
   #	ifdef Y
   		do_thing_with_Y_and_X();
   #	endif
   #elifdef Y
   #	ifndef Z
   #		define Z
   		do_thing_with_Y_and_Z();
   #	endif
   #elifndef Z
   	do_setup();
   #else
   	crash();
   #endif
   }
   
   
   
   void void_func() {
   }

2. pcpp --implicitly-undef --only-process=MACRO,Y main.c :

   #define MACRO
   #include "string.h"
   
   int main(void)
   {
   #ifdef X
   		do_thing();
   #elifdef Y
   #	ifndef Z
   #		define Z
   		do_thing_with_Y_and_Z();
   #	endif
   #elifndef Z
   	do_setup();
   #else
   	crash();
   #endif
   }
   
   #define string_implementation
   #include "string.h"

3. pcpp -DZ --only=MACRO,Z main.c:

   #include "string.h"
   
   int main(void)
   {
   #ifdef X
   #	ifdef Y
   		do_thing_with_Y_and_X();
   #	endif
   #elifdef Y
   #elifndef Z
   	do_setup();
   #else
   	crash();
   #endif
   }
   
   #define string_implementation
   #include "string.h"

4. pcpp -DX -DY --only=Y main.c

   #define MACRO
   #include "string.h"
   
   int main(void)
   {
   #ifdef X
   #	ifndef MACRO
   		do_thing();
   #	endif
   		do_thing_with_Y_and_X();
   #elifdef Y
   #	ifndef Z
   #		define Z
   		do_thing_with_Y_and_Z();
   #	endif
   #elifndef Z
   	do_setup();
   #else
   	crash();
   #endif
   }
   
   #define string_implementation
   #include "string.h"