使用 gcc 编译 C 时，预处理的 .i 文件中的数字是什么意思?

问题描述

我想了解编译过程.我们可以使用以下命令查看预处理器中间文件:

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

gcc -E hello.c -o hello.i

或

cpp hello.c > hello.i

我大致知道预处理器的作用，但我很难理解某些行中的数字.例如:

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

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.但是下面的数字有什么作用?

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?

推荐答案

文件名后面的数字是标志:

The numbers following the filename are flags:

1:表示新文件的开始.

1: This indicates the start of a new file.

2:这表示返回到一个文件(在包含另一个文件之后).

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

3:这表示以下文本来自系统头文件，因此应禁止某些警告.

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

4:这表示应将以下文本视为包含在隐式 extern "C" 块中.

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

来源:https://gcc.gnu.org/onlinedocs/cpp/预处理器-Output.html

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