c++ - 使用GCC对C文件进行部分预处理(不删除 “define”指令)

Question

如果我传递-E或-save-temps命令行参数，则GCC可以输出经过完全预处理的C++源文件。

我的问题是，我能以某种方式获取经过部分预处理的C++源文件，其中

a)消除了不满足＃if，＃ifdef和#ifndef条件的代码片段，

b)#include指令已解析(包括头文件)，等等

但

c)无法解析普通的#define指令？

(这将是必要的，而且真的很有帮助，因为我希望获得尽可能紧凑和可读的输出。
解决#if指令会缩短源代码，但是解决#define指令会使源代码的可读性降低，并且更加冗余。)

我试图创建一个尽可能紧凑的示例，以演示我想要实现的目标:

输入文件样本:

// header1.h
#ifndef header1_h
#define header1_h
int function1(int val) {
  return val + MYCONST;
}
#endif

// header2.h
#ifndef header2_h
#define header2_h
int function1(int val) {
  return val + val + MYCONST;
}
#endif

// main.c
#define MYCONST 1234
#define SETTING1
#ifdef SETTING1
  #include "header1.h"
#endif
#ifdef SETTING2
  #include "header2.h"
#endif
int main(void) {
  int retVal = function1(99);
}

预期产量:

// main.i (GCC preprocessing output)
#define MYCONST 1234 // I would like to see the definition of MYCONST here
#define SETTING1
#define header1_h
int function1(int val) {
  return val + MYCONST; // I would like to see MYCONST here instead of the resolved value
}
int main(void) {
  int retVal = function1(99);
}

Answer 1

gcc有一个 -fdirectives only 选项，它可以完成您所需的操作:

-fdirectives-only

When preprocessing, handle directives, but do not expand macros.

The option’s behavior depends on the -E and -fpreprocessed options.

With -E, preprocessing is limited to the handling of directives such as #define, #ifdef, and #error. Other preprocessor operations, such as macro expansion and trigraph conversion are not performed. In addition, the -dD option is implicitly enabled.

With -fpreprocessed, predefinition of command line and most builtin macros is disabled. Macros such as __LINE__, which are contextually dependent, are handled normally. This enables compilation of files previously preprocessed with -E -fdirectives-only.

With both -E and -fpreprocessed, the rules for -fpreprocessed take precedence. This enables full preprocessing of files previously preprocessed with -E -fdirectives-only.

在您的情况下，应将其称为

 % gcc -fdirectives-only -E -o main.i main.c

但是您得到的定义(内部定义的)，空行和#line行比您想要的更多。