GCC 选项 -save-temps 个数字在 header 个文件之后

Question

当我使用 -save-temps 选项在 gcc 上编译代码时，存储预处理输出的结果 filename.i 包含如下行：

#44 "/usr/include/stdio.h" 3 4
struct _IO_FILE;

其中 44 是 /usr/include/stdio.h 中包含代码 struct _IO_FILE; 的行号。我想知道 header 名字后面的 3 4 是什么。我在 man gcc 中搜索过，但没有找到解释。

Answer 1

https://gcc.gnu.org/onlinedocs/cpp/Preprocessor-Output.html#Preprocessor-Output:

Source file name and line number information is conveyed by lines of the form

# linenum filename flags

These are called linemarkers. They are inserted as needed into the output (but never within a string or character constant). They mean that the following line originated in file filename at line linenum. filename will never contain any non-printing characters; they are replaced with octal escape sequences.

After the file name comes zero or more flags, which are 1, 2, 3, or 4. If there are multiple flags, spaces separate them. Here is what the flags mean:

• 1 - This indicates the start of a new file.

• 2 - This indicates returning to a file (after having included another file).

• 3 - This indicates that the following text comes from a system header file, so certain warnings should be suppressed.

• 4 - This indicates that the following text should be treated as being wrapped in an implicit extern "C" block.