Debugging information in GCC preprocessor output

Question

I was inspecting the preprocessed output generated by GCC, and I see a lot of these in the .i file that I generated using the -save-temps flag:

# 8 "/usr/include/i386-linux-gnu/gnu/stubs.h" 2 3 4

What do the numbers before and after the absolute path of stubs.h mean? It seems to be some kind of debugging information that is inserted by the preprocessor and allows the compiler to issue error messages referring to this information. These lines do not affect the program itself, but what specifically is each number for?

Ulrich Dangel · Accepted Answer · 2013-05-04 12:51:06Z

5

Based on the documentation the number before the filename is the line number. The numbers after the file name are a flag and mean the following:

1 indicates the start of a new file.
2 indicates returning to a file (after having included another file).
3 indicates that the following text comes from a system header file, so certain warnings should be suppressed.
4 indicates that the following text should be treated as being wrapped in an implicit extern "C" block.

answered May 4, 2013 at 12:51

Ulrich Dangel

4,6653 gold badges24 silver badges30 bronze badges

Sign up to request clarification or add additional context in comments.

8 Comments

ArunMKumar Over a year ago

and what line number would it signify because i see many files included with the same line number... am i missing some obvious thing here?

ArunMKumar Over a year ago

# 1 "/usr/include/stdio.h" 1 3 4, # 28 "/usr/include/stdio.h" 3 4, # 1 "/usr/include/features.h" 1 3 4, # 324 "/usr/include/features.h" 3 4

Ulrich Dangel Over a year ago

@ArunKumar Based on your flags this just shows that a new file was opened

Ulrich Dangel Over a year ago

@ArunKumar no, it is exactly the same. # 1 "/usr/include/stdio.h" 1 3 4 means /usr/include/stdio.h was opened and we are at line number 1

Ulrich Dangel Over a year ago

@ArunKumar depends on the context but line number of the referenced file, in my example /usr/include/stdio.h

|

Collectives™ on Stack Overflow

Debugging information in GCC preprocessor output

1 Answer 1

8 Comments

Your Answer

Linked

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

8 Comments

Your Answer

Sign up or log in

Post as a guest

Linked

Related