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，GCC 可以输出完全预处理的 C++ 源文件。

我的问题是，我能否以某种方式获得部分预处理的 C++ 源文件，其中

a) 不满足#if、#ifdef、#ifndef条件的代码片段被剔除，

b) #include 指令已解析（包含头文件）等

但是

c) 普通的#define 指令未解析？

（这将是必要的并且非常有帮助，因为我希望获得尽可能紧凑和可读的输出。解析#if 指令会缩短源代码，但解析#define 指令会使源代码的可读性降低且冗余。）

我已尝试创建一个尽可能紧凑的示例，以演示我想要实现的目标：

示例输入文件：

// 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);
}

预期输出：

// 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 有一个选项 -fdirectives only 可以做一些接近你想要的事情：

-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.

在你的情况下，它应该被称为

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

但是您得到的定义（那些内部定义的）、空行和 #line 行比您要求的要多。

使用 GCC 对 C 文件进行部分预处理（不删除 "define" 指令）

Partial preprocessing of C files with GCC (not removing "define" directives)

c++

gcc

c-preprocessor