使用gcc编译C时，预处理的.i文件中的数字意味着什么？ [英] What do the numbers mean in the preprocessed .i files when compiling C with gcc?

问题描述

我试图理解编译过程。我们可以看到预处理器中间文件：

  gcc -E hello.c -o hello.i 
  

或

  cpp hello.c> hello.i 
  

我大概知道预处理程序的功能，但是我很难理解某些数字线。例如：

 ＃1/usr/include/stdc-predef.h1 3 4 
＃1 <命令行> 中2 
＃1hello.c
＃1/usr/include/stdio.h1 3 4 
＃27/usr/include/stdio.h3 4 
＃1/usr/include/features.h1 3 4 
＃374/usr/include/features.h3 4 
  

这些数字可以帮助调试器显示行号。所以我对第一列的猜测是列＃2文件的行号。但是下面的数字是做什么的？

解决方案

文件名后面的数字是标志：

1：表示新文件的开始。

2：表示返回到文件（包含另一个文件后） p>

3：这表示以下文本来自系统头文件，因此应禁止某些警告。

4：这表示应将以下文本视为包含在隐式 externC块中。

资料来源： https ：//gcc.gnu.org/onlinedocs/cpp/Preprocessor-Output.html

I am trying to understand the compiling process. We can see the preprocessor intermediate file by using:

gcc -E hello.c -o hello.i

or

cpp hello.c > hello.i

I roughly know what the preprocessor does, but I have difficulties understanding the numbers in some of the lines. For example:

 # 1 "/usr/include/stdc-predef.h" 1 3 4
 # 1 "<command-line>" 2
 # 1 "hello.c"
 # 1 "/usr/include/stdio.h" 1 3 4
 # 27 "/usr/include/stdio.h" 3 4
 # 1 "/usr/include/features.h" 1 3 4
 # 374 "/usr/include/features.h" 3 4

The numbers can help debugger to display the line numbers. So my guess for the first column is the line number for column #2 file. But what do the following numbers do?

解决方案

The numbers following the filename are flags:

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.

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

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