Source file inclusion

 

C++

Language

Standard library headers

Concepts

Utilities library

Strings library

Containers library

Algorithms library

Iterators library

Numerics library

Input/output library

Localizations library

Regular expressions library (C++11)

Atomic operations library (C++11)

Thread support library (C++11)

 

C++ language

General topics
Preprocessor Comments Keywords	Escape sequences History of C++
Flow control
Conditional execution statements
if statement	switch statement
Iteration statements
for loop range-for loop (C++11)	while loop do-while loop
Jump statements
continue statement break statement	goto statement return statement
Functions
function declaration
lambda function declaration
function template
inline specifier
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noexcept specifier (C++11)
Exceptions
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Types
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decltype specifier (C++11)
Specifiers
cv specifiers
storage duration specifiers
constexpr specifier (C++11)
auto specifier (C++11)
alignas specifier (C++11)
Initialization
default initialization value initialization zero initialization copy initialization direct initialization	aggregate initialization list initialization (C++11) constant initialization reference initialization

Literals
integer literals character literals floating-point literals string literals	boolean literals nullptr (C++11) user-defined (C++11)
Expressions
value categories order of evaluation	operators operator precedence
alternative representations
Utilities
Types
typedef declaration
type alias declaration (C++11)
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new expression	delete expression
Classes
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Class-specific function properties
virtual function override specifier (C++11) final specifier (C++11)	explicit (C++11) static
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Templates
class template
function template
template specialization
parameter packs (C++11)
Miscellaneous
Inline assembly

 

Preprocessor

#if#ifdef#ifndef#else#elif#endif

#define#undef#,## operators

#include

#error

#pragma

#line

 

Includes other source file into current source file at the line immediately after the directive .

Syntax

#include <filename>	(1)
#include "filename"	(2)

Explanation

Includes source file, identified by filename into the current source file at the line immediately after the directive. In the case the file is not found, program is ill-formed.

1) searches only standard include directories. The standard C++ library, as well as standard C library, is implicitly included in standard include directories. The standard include directories can be controlled by the user through compiler options.

2) firstly searches the directory where the current file resides and, only if the file is not found, searches the standard include directories.

Any preprocessing tokens (macro constants or expressions) are permitted as arguments to #include as long as they expand to a sequence of characters surrounded by < > or " ".

Example

Run this code

#ifndef TEXT
    #include <iostream>
 
    int main()
    {
    #define TEXT "Hello, world!"
    #include __FILE__
    #define TEXT "Hello again!"
    #include __FILE__
 
    }
#else
    std::cout << TEXT << '\n';
    #undef TEXT
#endif

Output:

Hello, world!
Hello again!

See also

cpp/header

a list of C++ Standard Library header files