The #include preprocessor directive in C inserts the contents of an external source file into the current source file, copying its contents to the corresponding location in the current source file. Mainly used to include header files that contain declarations needed in the code. For example, #include <iostream> includes standard input/output functions.

#include in C

In C, #include is a preprocessor directive used to Inserts the contents of an external source file into the current source file.

Function

The function of include is to copy the contents of the specified source file to the corresponding location of the current source file, as if the contents were written directly to the current source file. . Source files can be header files (containing declarations of functions, classes, and macros) or other source files.

Syntax

The general syntax of include is:

<code class="cpp">#include <source_file></code>

Where, <source_file> specifies the source file to be included path and file name. Paths can be absolute or relative.

Usage

include is mainly used to include header files, which usually contain declarations needed in the code. For example, to use the standard input/output functions, you need to include the <iostream> header file:

<code class="cpp">#include <iostream></code>

scope

include directive affects only The file it resides in. It does not affect other source files or header files.

Note

• Multiple inclusions: Multiple inclusions of the same source file will only be included once.
• Search path: The compiler searches for source files in the specified path and the system default path according to specific rules.
• Conditional inclusion: #The if, #elif, and #else directives can be used to conditionally include or exclude source files.

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