Angle Brackets vs. Double Quotes: How Should I Include Header Files in C ?

Difference between Angle Bracket <> and Double Quotes "" While Including Header Files in C

Introduction

When including header files in C , programmers can choose between using angle brackets <> or double quotes "". This decision influences the search path for the header file.

Angle Bracket (<>) Usage

Headers included using angle brackets are typically system headers located in standard include directories. These directories are defined by the compiler and include essential headers for the C standard library and other system components. By using angle brackets, the compiler searches these directories first.

Double Quote ("") Usage

Headers included using double quotes are typically user-defined headers or headers located in custom directories. When using double quotes, the compiler first searches the current working directory for the header file. If the file is not found there, it proceeds to search the system include directories.

How to Decide

The choice between angle brackets and double quotes depends on the location of the header file you want to include:

• Angle brackets (<>): Use for system headers that are part of the standard library or other system components.
• Double quotes ("): Use for user-defined headers or headers that are located in non-standard include directories.

Implementation-Specific Behavior

Note that the search path behavior can be implementation-specific. Some compilers may prioritize the current working directory over system headers, even when using angle brackets. Refer to your compiler documentation for specific details.

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