C Header Files: Angle Brackets vs. Double Quotes – When to Use Which?

#include Directive: Angle Brackets (< >) vs. Double Quotes (" ")

When including header files in C , you have the option of using either angle brackets (< >) or double quotes (" ") to specify the file's location. This choice has implications depending on the compiler and the location of the header file.

Angle Brackets (< >)

• Prioritize system headers: Headers that are part of the compiler's standard library or operating system are typically included using angle brackets.
• Implementation-defined search path: The exact locations where the compiler looks for system headers is determined by the compiler itself.

Double Quotes (" ")

• Prioritize current working directory: Headers that are located in the current working directory are typically included using double quotes.
• Custom search path: Some compilers allow you to specify additional search paths for header files included with double quotes. If these paths are not specified, the compiler will first search the current working directory.

Summary

In general, it is recommended to use angle brackets (< >) to include system headers and double quotes (" ") to include headers located in your own project or in the current working directory. The choice between angle brackets and double quotes can also influence the order in which the compiler searches for header files.

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