Where Are Include Files Stored - Ubuntu Linux, Gcc

Where are include files stored - Ubuntu Linux, GCC

See here: Search Path

Summary:

#include <stdio.h>

When the include file is in brackets the preprocessor first searches in paths specified via the -I flag. Then it searches the standard include paths (see the above link, and use the -v flag to test on your system).

#include "myFile.h"

When the include file is in quotes the preprocessor first searches in the current directory, then paths specified by -iquote, then -I paths, then the standard paths.

-nostdinc can be used to prevent the preprocessor from searching the standard paths at all.

Environment variables can also be used to add search paths.

When compiling if you use the -v flag you can see the search paths used.

Where does gcc look for C and C++ header files?

`gcc -print-prog-name=cc1plus` -v

This command asks gcc which C++ preprocessor it is using, and then asks that preprocessor where it looks for includes.

You will get a reliable answer for your specific setup.

Likewise, for the C preprocessor:

`gcc -print-prog-name=cpp` -v

Where is Location stdio.h file in Linux of gcc.7.2 compiler?

You are looking in the wrong location. stdio.h is not located in /usr/lib/gcc but in /usr/include

<> Is basically a shortcut to /usr/include (or any directory you specify after the -I compiler flag) in C/C++. So

#include <myheader.h>

would include /usr/include/myheader.h and

#include <file/otherheader.h> 

Would include /usr/include/file/otherheader.h
This means that since you normally include stdio.h with

#include <stdio.h>

the location would be /usr/include/stdio.h

What are the GCC default include directories?

In order to figure out the default paths used by gcc/g++, as well as their priorities, you need to examine the output of the following commands:

1. For C:

    gcc -xc -E -v -

2. For C++:

    gcc -xc++ -E -v -

The credit goes to Qt Creator team.

where are the head file in /usr/include from? Linux kernel code Or Gcc

They both come from GlibC; usually kernel header files are in /usr/include/linux and other subdirs, while gcc includes are located elsewhere (like /usr/lib/<arch>/<version>/include)

How to let gcc compiler know where a certain file is

In gcc, the -I option is used for adding a directory to the set of directories to search for header files, and the -L option is used for adding a directory to the set of directories to search for libraries. Since you're not explicitly linking in any libraries, you shouldn't need the -L option in this case.

gcc -I/usr/local/ssl/include -o file file.c

If you were linking in libraries, something like the following format should work, assuming that file.c calls a function in libmyLib.a:

gcc -I/usr/local/ssl/include -o file file.c -L/path/to/my/library -lmyLib

See this question for more details regarding library linking order.

How to add a default include path for GCC in Linux?

Try setting C_INCLUDE_PATH (for C header files) or CPLUS_INCLUDE_PATH (for C++ header files).

As Ciro mentioned, CPATH will set the path for both C and C++ (and any other language).

More details in GCC's documentation.

How can I find the header files of the C programming language in Linux?

gcc -H ... will print the full path of every include file as a side-effect of regular compilation. Use -fsyntax-only in addition to get it not to create any output (it will still tell you if your program has errors). Example (Linux, gcc-4.7):

$ cat > test.c
#include <stdbool.h>
#include <stdio.h>
^D
$ gcc -H -fsyntax-only test.c
. /usr/lib/gcc/x86_64-linux-gnu/4.7/include/stdbool.h
. /usr/include/stdio.h
.. /usr/include/features.h
... /usr/include/x86_64-linux-gnu/bits/predefs.h
... /usr/include/x86_64-linux-gnu/sys/cdefs.h
.... /usr/include/x86_64-linux-gnu/bits/wordsize.h
... /usr/include/x86_64-linux-gnu/gnu/stubs.h
.... /usr/include/x86_64-linux-gnu/bits/wordsize.h
.... /usr/include/x86_64-linux-gnu/gnu/stubs-64.h
.. /usr/lib/gcc/x86_64-linux-gnu/4.7/include/stddef.h
.. /usr/include/x86_64-linux-gnu/bits/types.h
... /usr/include/x86_64-linux-gnu/bits/wordsize.h
... /usr/include/x86_64-linux-gnu/bits/typesizes.h
.. /usr/include/libio.h
... /usr/include/_G_config.h
.... /usr/lib/gcc/x86_64-linux-gnu/4.7/include/stddef.h
.... /usr/include/wchar.h
... /usr/lib/gcc/x86_64-linux-gnu/4.7/include/stdarg.h
.. /usr/include/x86_64-linux-gnu/bits/stdio_lim.h
.. /usr/include/x86_64-linux-gnu/bits/sys_errlist.h

The dots at the beginning of each line count how deeply nested the #include is.

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