linux header file loading sequence

Refer to the header file search path under Linux

“header.h”

 #include "header.h"

When the same file exists in each directory, first find which one to use. The loading sequence is as follows:

1. Current directory

2. The directory specified by the parameter -I when gcc is compiled

3. Environment variable C_INCLUDE_PATH (C++ uses CPLUS_INCLUDE_PATH)

4. System default directory

   • /usr/include
   • /usr/local/include
   • /usr/include/x86_64-linux-gnu

<header.h>

#include <header.h>

When the same file exists in each directory, first find which one to use. But the current directory will not be searched !

1. The directory specified by the parameter -I when gcc is compiled

2. Environment variable C_INCLUDE_PATH (C++ uses CPLUS_INCLUDE_PATH)

3. System default directory

   • /usr/include
   • /usr/local/include
   • /usr/include/x86_64-linux-gnu

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You can view the LIBRARY_PATH and INCLUDE paths of gcc through the following command

echo 'main(){}' | gcc -E -v -