C 预处理文件中这些不熟悉的行是什么？

Question

这是 GNU cpp 在 C 语言的 Hello World 程序上的输出。我想知道这些行是什么意思？ #个数Header_File_Location[个数]

# 1 "hello.c"
# 1 "<built-in>"
# 1 "<command-line>"
# 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
# 1 "/usr/include/x86_64-linux-gnu/sys/cdefs.h" 1 3 4
# 385 "/usr/include/x86_64-linux-gnu/sys/cdefs.h" 3 4
# 1 "/usr/include/x86_64-linux-gnu/bits/wordsize.h" 1 3 4
# 386 "/usr/include/x86_64-linux-gnu/sys/cdefs.h" 2 3 4
# 375 "/usr/include/features.h" 2 3 4
# 398 "/usr/include/features.h" 3 4
# 1 "/usr/include/x86_64-linux-gnu/gnu/stubs.h" 1 3 4
# 10 "/usr/include/x86_64-linux-gnu/gnu/stubs.h" 3 4
# 1 "/usr/include/x86_64-linux-gnu/gnu/stubs-64.h" 1 3 4
# 11 "/usr/include/x86_64-linux-gnu/gnu/stubs.h" 2 3 4
# 399 "/usr/include/features.h" 2 3 4
# 28 "/usr/include/stdio.h" 2 3 4





# 1 "/usr/lib/gcc/x86_64-linux-gnu/4.8/include/stddef.h" 1 3 4
# 212 "/usr/lib/gcc/x86_64-linux-gnu/4.8/include/stddef.h" 3 4
typedef long unsigned int size_t;
# 34 "/usr/include/stdio.h" 2 3 4

# 1 "/usr/include/x86_64-linux-gnu/bits/types.h" 1 3 4
# 27 "/usr/include/x86_64-linux-gnu/bits/types.h" 3 4
# 1 "/usr/include/x86_64-linux-gnu/bits/wordsize.h" 1 3 4
# 28 "/usr/include/x86_64-linux-gnu/bits/types.h" 2 3 4


typedef unsigned char __u_char;
typedef unsigned short int __u_short;
typedef unsigned int __u_int;
typedef unsigned long int __u_long;

这些是某种依赖关系吗？如果是，那么在什么？行号？

Answer 1

这些是行号指令，告诉编译器translation unit中源代码的下一部分来自哪一行和文件。

这就是编译器在预处理后报告包含的头文件中的错误的方式。

Answer 2

来自 gcc documentation:

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.

C 预处理文件中这些不熟悉的行是什么？

What are these unfamiliar lines in the C preprocessed file?

c

c++

linux

gnu

compilation