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)

Technical Specifications

 

C++ language

General topics
Preprocessor Comments	Keywords Escape sequences
Flow control
Conditional execution statements
if	switch
Iteration statements (loops)
for range-for (C++11)	while do-while
Jump statements
continue - break	goto - return
Functions
Function declaration
Lambda function declaration
inline specifier
Exception specifications (deprecated)
noexcept specifier (C++11)
Exceptions
throw-expression	try-catch block
Namespaces
Namespace declaration	Namespace aliases
Types
Fundamental types Enumeration types Function types	Compound types Union types
Specifiers
decltype (C++11) auto (C++11) alignas (C++11)	const/volatile constexpr (C++11)
Storage duration specifiers
Initialization
Default initialization Value initialization Zero initialization Copy initialization Direct initialization	Aggregate initialization List initialization (C++11) Constant initialization Reference initialization

Expressions
Value categories Order of evaluation	Operators Operator precedence
Alternative representations
Literals
Boolean - Integer - Floating-point
Character - String - nullptr (C++11)
User-defined (C++11)
Utilities
Attributes (C++11)
Types
typedef declaration
Type alias declaration (C++11)
Casts
Implicit conversions - Explicit conversions
static_cast - dynamic_cast
const_cast - reinterpret_cast
Memory allocation
new expression	delete expression
Classes
Class declaration Initializer lists this pointer	Access specifiers friend specifier
Class-specific function properties
Virtual function override specifier (C++11) final specifier (C++11)	explicit (C++11) static
Special member functions
Default constructor Copy constructor Move constructor (C++11)	Copy assignment Move assignment (C++11) Destructor
Templates
Class template Function template	Template specialization Parameter packs (C++11)
Miscellaneous
Inline assembly	History of C++

 

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
C documentation for Source file inclusion