This is an output of the GNU cpp on a Hello World program in C. I am wondering what do these lines mean? # Number Header_File_Location [Numbers]
# 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;
Are these some kind of dependencies? If yes, then on what? Line numbers?
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Answer
Those are line number directives, and tells the compiler what line and file the next part of the source in the translation unit come from.
That’s how the compiler can report errors in included header files after preprocessing.