User-defined literals (since C++11)

 

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

 

Expressions

General

value categories (lvalue, rvalue, xvalue)

order of evaluation (sequence points)

constant expressions

unevaluated expressions

primary expressions

lambda-expression(C++11)

Literals

integer literals

floating-point literals

boolean literals

character literals including escape sequences

string literals

null pointer literal(C++11)

user-defined literal(C++11)

Operators

Assignment operators: a=b, a+=b, a-=b, a*=b, a/=b, a%=b, a&=b, a|=b, a^=b, a<<=b, a>>=

Increment and decrement: ++a, --a, a++, a--

Arithmetic operators: +a, -a, a+b, a-b, a*b, a/b, a%b, ~a, a&b, a|b, a^b, a<<b, a>>b

Logical operators: a||b}, a&&b, !a

Comparison operators: a==b, a!=b, a<b, a>b, a<=b, a>=b

Member access operators: a[b], *a, &a, a->b, a.b, a->*b, a.*b

Other operators: a(...), a,b, (T)a, a?b:c

Alternative representations of operators

Precedence and associativity

new-expression

delete-expression

throw-expression

alignof

sizeof

sizeof...(C++11)

typeid

noexcept(C++11)

Operator overloading

Conversions

Implicit conversions

const_cast

static_cast

reinterpret_cast

dynamic_cast

Explicit conversions (T)a, T(a)

User-defined conversion

 

C++11 introduced the ability to add custom suffixes to literals in order to provide different values. Literal suffixes can be overloaded in a way very similar to operators.

Syntax

decl return operator"" name ( unsigned long long n ) { body }
decl return operator"" name ( long double d ) { body }
decl return operator"" name ( const char* cstr ) { body }
decl return operator"" name ( char_type c ) { body }
decl return operator"" name ( constchar_type * str, size_t sz ) { body }
template <char...>decl return operator"" name ( ){ body }

Explanation

char_type	-	one of char, char16_t, char32_t,wchar_t
decl	-	Declaration specifier sequence, can contain keywords as constexpr or inline
return	-	Return value
name	-	A valid C++ identifier, prefixed with an underscore. Identifiers without underscore are reserved for future use
n	-	Value resulting from an integral literal
d	-	Value resulting from a floating-point literal
c	-	Value resulting from a character literal
cstr	-	Null-terminated string as parsed by the compiler, for integer and floating point literals
str/sz	-	Buffer and size from a string literal
body	-	Function body

Examples

Run this code

#include <iostream>
 
// used as conversion
constexpr long double operator"" _deg ( long double deg )
{
    return deg*3.141592/180;
}
 
// used with custom type
struct mytype
{
    mytype ( unsigned long long m):m(m){}
    unsigned long long m;
};
mytype operator"" _mytype ( unsigned long long n )
{
    return mytype(n);
}
 
// used for side-effects
void operator"" _print ( const char* str )
{
    std::cout << str;
}
 
int main(){
    double x = 90.0_deg;
    std::cout << std::fixed << x << '\n';
    mytype y = 123_mytype;
    std::cout << y.m << '\n';
    0x123ABC_print;
}

Output:

1.570796
123
0x123ABC