问题
When I compile a very simple source file with gcc I don\'t have to specify the path to standard include files such as stdio or stdlib.
How does GCC know how to find these files?
Does it have the /usr/include path hardwired inside, or it will get the paths from other OS components?
回答1:
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:
- For C:
gcc -xc -E -v -
- For C++:
gcc -xc++ -E -v -
The credit goes to Qt Creator team.
回答2:
There is a command with a shorter output, which allows to automatically cut the include pathes from lines, starting with a single space:
$ echo | gcc -Wp,-v -x c++ - -fsyntax-only
ignoring nonexistent directory "/usr/lib/gcc/x86_64-redhat-linux/4.8.2/include-fixed"
ignoring nonexistent directory "/usr/lib/gcc/x86_64-redhat-linux/4.8.2/../../../../x86_64-redhat-linux/include"
#include "..." search starts here:
#include <...> search starts here:
/usr/lib/gcc/x86_64-redhat-linux/4.8.2/../../../../include/c++/4.8.2
/usr/lib/gcc/x86_64-redhat-linux/4.8.2/../../../../include/c++/4.8.2/x86_64-redhat-linux
/usr/lib/gcc/x86_64-redhat-linux/4.8.2/../../../../include/c++/4.8.2/backward
/usr/lib/gcc/x86_64-redhat-linux/4.8.2/include
/usr/local/include
/usr/include
End of search list.
The credit goes to the libc++ front-page.
回答3:
Here is an article describing the gcc search paths: http://www.network-theory.co.uk/docs/gccintro/gccintro_21.html
In addition, you can specify extra search paths with the -I switch. You can do this from the command line or in your makefile.
回答4:
Just run the following to list the default search paths:
$(gcc -print-prog-name=cc1) -v
来源：https://stackoverflow.com/questions/4980819/what-are-the-gcc-default-include-directories