How Does GCC Find Standard Include Files?

Exploring GCC's Default Include Directories

When compiling a C or C program, developers often rely on standard include files without explicitly specifying their paths. This raises the question: how does GCC locate these files?

To determine the default paths and their priorities, execute the following commands:

echo | gcc -xc -E -v -

for C, or

echo | gcc -xc++ -E -v -

for C .

The output of these commands contains a wealth of information, including the paths used by GCC.

Flags Breakdown:

• -x specifies the language (C or C )
• -E runs only the preprocessor, excluding compilation
• -v prints the executed commands
• - serves as the input file, with echo | providing an empty string

Path Priority:

The output displays the paths in descending order of priority, with the highest-priority path listed first. This order determines which path GCC will search for include files first.

Credit:

Special thanks to the Qt Creator team for providing this insightful method.

Additional Resources:

For further explanation, refer to the following resource:

• [explainshell.com/explain?cmd=echo | gcc -xc -E -v -]()

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