CODEWITHSUNDEEP
linuxgcc
apadana
apadana

Reputation: 722

Where are C header files in gcc 7?

On a linux server which has an old version of gcc (4.4.7), I built gcc 7.4.0 from source code and installed it in a directory within the home.

Now I'm not sure how to use it. The directory includes some subdirectories, one named "include". Inside it there is a folder named "c++". It includes another folder named "7.4.0". But where are C header files? Did the installer install them in a different place? Which address should I provide with -I option when compiling a C program?

Unfortunately I don't have the gcc source directory anymore.

Upvotes: 1

Views: 2216

Answers (1)

emacs drives me nuts
emacs drives me nuts

Reputation: 4012

But where are C header files?

You can find out where gcc expects them by

echo '#include <stdio.h>' | gcc -xc - -H -v -fsyntax-only

The -v part will print the search paths like

#include "..." search starts here:
#include <...> search starts here:
 /home/...
 /usr/local/include
 ...

The -H part will print which header files art actually being used:

. /usr/include/stdio.h
.. /usr/include/x86_64-linux-gnu/bits/libc-header-start.h
... /usr/include/features.h
etc.

The command line with echo above can be used if you have no source file handy. In the case you are interested how, say, module.c behaves, you can use -v and -H when compiling that module, e.g.

gcc module.c -H -v -o module.elf

Which address should I provide with -I option when compiling a C program?

Paths where headers of your C project are located if they are not in the current directory. For simple projects you do not need -I: Compiling module.c will find #include "module.h" if both files are located in the same directory.

The right option to specify extra system header path would be -isystem, however an installation is supposed to find the system headers without any further hacking, i.e. the supposed search paths must be listed under #include <...> search starts here: and without setting -isystem.

Did the installer install them in a different place?

libc implementations (like glibc or Newlib) are not part of GCC whereas the C++ library libstdc++-v3 is hosted with GCC and is built when GCC is configured with --enable-languages=c++. The location of the C-libraries and C-headers should be worked out by configure.

For some C-libraries like Newlib, GCC supports in-tree builds so that these target libraries will be contained in the installation and the paths are set appropriately. Building glibc however is much more complicated.

Upvotes: 4

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