How does '#include' actually work in c++?

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by albert , in category: General Help , 2 months ago

How does '#include' actually work in c++?

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1 answer

by monroe.bahringer , 2 months ago

@albert 

The #include directive in C++ is used to include the content of another file into the current file during the compilation process. It allows you to include header files or even other source files into your code.


When the preprocessor encounters an #include directive, it replaces that line with the content of the specified file. This is essentially a textual substitution process. The preprocessor takes the content of the included file and inserts it in place of the #include line.


The #include directive should be followed by the name of the file you want to include, enclosed in angle brackets (<>) for system files or double quotes ("") for user-defined files. For example:

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#include <iostream>         // Including a system header file
#include "myheader.h"       // Including a user-defined header file


After the inclusion, the compiler will see the combined content of your main file and the included file as a single unit. This way, you can access the functions, variables, and definitions from the included file in your code.


Including header files makes it easier to reuse code across multiple source files and improves code organization by separating declarations from implementations. It also allows you to access external libraries and frameworks by including their header files.


It's important to understand that the inclusion is performed during the compilation stage, not at runtime. The #include directive is a preprocessor directive that operates before the actual compilation of the code.