Preprocessor

 

C++

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C++ language

General topics
Preprocessor
Comments
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Escape sequences
History of C++
Flow control
Conditional execution statements
if statement	switch statement
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for loop range-for loop (C++11)	while loop do-while loop
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continue statement break statement	goto statement return statement
Functions
function declaration
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function template
inline specifier
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noexcept specifier (C++11)
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throw expression	try-catch block
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namespace declaration	namespace aliases
Types
fundamental types compound types enumeration types	union types function types
decltype specifier (C++11)
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auto specifier (C++11)
alignas specifier (C++11)
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Expressions
value categories order of evaluation	operators operator precedence
alternative representations
Utilities
Types
typedef declaration
type alias declaration (C++11)
attributes (C++11)
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implicit conversions
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C-style and functional cast
Memory allocation
new expression	delete expression
Classes
class declaration this pointer access specifiers	friend specifier initializer lists
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virtual function override specifier (C++11) final specifier (C++11)	explicit (C++11) static
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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

 

Preprocessor

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

#define #undef #,## operators

#include

#warning

#error

#pragma

#line

 

The preprocessor runs before the compilation begins. The result of preprocessing is single file which is then passed to the actual compiler.

Directives

The preprocessing directives control the behavior of the preprocessor. Each directive occupies one line and has the following format:

• # character
• preprocessing instruction (one of define, undef, include, if, ifdef, ifndef, else, elif, endif, line, error, warning, pragma)
• arguments (depends on the instruction)
• line break

The null directive (# followed by a line break) is allowed and has no effect.

Capabilities

The preprocessor has the source file translation capabilities:

• conditionally compile of parts of source file (controlled by directive #if, #ifdef, #ifndef, #else, #elif and #endif).
• replace text macros while possibly concatenating or quoting identifiers (controlled by directives #define and #undef, and operators # and ##)
• include other files (controlled by directive #include)
• cause a warning (controlled by directive #warning)
• cause an error (controlled by directive #error)

The following aspects of the preprocessor can be controlled:

• implementation defined behavior (controlled by directives #pragma)
• file name and line information available to the preprocessor (controlled by directives #line)