理解C++中#include ＜iostream＞

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• #include

From 《C++ Library reference 概览》, include come from ‘algorithm -> merge -> includes’.

From geeksforgeeks, #include is a way of including a standard or user-defined file in the program and is mostly written at the beginning of any C/C++ program. This directive is read by the preprocessor and orders it to insert the content of a use-defined or system header file into the following program.

There are two types of file that can be included using #include:

1. Header File or Standard files
2. User-define files

And there are two syntax using the #include command:

1. #include "user-defined-file"

   When using the double quotes(" "), the preprocessor access the current directory in which the source “user-defined-file” is located.

   This type is mainly used to access any header files of the user’s program or user-defined files.

2. #include <header_file>

   While importing file using angular bracket(<>), the preprocessor uses a predetermined directory path to access the file. It is mainly used to access system header files located in the standard system directories.

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