CODEWITHSUNDEEP
clinuxheader
Some Name
Some Name

Reputation: 9521

What is the difference between /usr/include/linux and /usr/include/x86_64-linux-gnu/

I'm very new to native C programming and now I'm trying to configure my IDE to set up include paths correctly. Since I would like to navigate by sys/xxx.h files I added

/usr/include/x86_64-linux-gnu/

to my include path. But there is also /usr/include/linux which seems contains the same headers also. So what is the difference between them? And which one should I use actually?

Upvotes: 2

Views: 1365

Answers (1)

zwol
zwol

Reputation: 140589

I can tell you immediately that the directories /usr/include/linux and /usr/include/asm should never be included in a list of system header directories. The headers in those directories are meant to be used as #include <linux/whatever.h> or #include <asm/whatever.h>, not as #include <whatever.h>.

The rest of the answer to this question depends on exactly which "distribution" of Linux you are using, so I can't just say it. Fortunately, there is a way to get the compiler to tell you. Run this command (exactly as shown) in a terminal window:

LC_ALL=C gcc -v -xc -E /dev/null 2>&1 | 
    sed -ne '/search starts here/,/End of search list/p'

You will get output that looks something like this, but the details may be slightly different:

#include "..." search starts here:
#include <...> search starts here:
 /usr/lib/gcc/x86_64-linux-gnu/8/include
 /usr/local/include
 /usr/lib/gcc/x86_64-linux-gnu/8/include-fixed
 /usr/include/x86_64-linux-gnu
 /usr/include
End of search list.

The directories listed are the directories you should configure your IDE to look for system headers in, for purpose of looking up declarations and whatnot. However, you should not configure your IDE to pass any of these directories to the compiler as -I directories. It already knows to use them, it doesn't need to be told again, and telling it again can mess things up (for instance, the order of the above directories matters).

As an application programmer you don't need to worry about which headers "belong" in which directories. That's entirely the compiler and C library developers and Linux distribution maintainers' task.

Upvotes: 7

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