Isinf

Defined in header <cmath>.

Description

Determines if the given floating-point number num is a positive or negative infinity.
​The library provides overloads for all cv-unqualified floating-point types as the type of the parameter num  (since C++23).

​Additional Overloads are provided for all integer types, which are treated as double.

Declarations

C++23

// 1)
constexpr bool isinf( /* floating-point-type */ num );

Additional Overloads

// 2)
template< class Integer >
constexpr bool isinf( Integer num );

C++11

// 1)
bool isinf( float num );
// 2)
bool isinf( double num );
// 3)
bool isinf( long double num );

Additional Overloads

// 4)
template< class Integer >
bool isinf( Integer num );

Parameters

​num - floating-point or integer value

Return value

true if num is infinite, false otherwise.

Notes

The additional overloads are not required to be provided exactly as Additional Overloads. They only need to be sufficient to ensure that for their argument num of integer type,
std::isinf(num) has the same effect as std::isinf(static_cast<double>(num)).

Examples

#include <cfloat>
#include <cmath>
#include <iostream>
#include <limits>
 
int main()
{
    const double max = std::numeric_limits<double>::max();
    const double inf = std::numeric_limits<double>::infinity();
 
    std::cout 
        << std::boolalpha
        << "isinf(NaN) = " 
        << std::isinf(NAN) << '\n'
        << "isinf(Inf) = " 
        << std::isinf(INFINITY) << '\n'
        << "isinf(max) = " 
        << std::isinf(max) << '\n'
        << "isinf(inf) = " 
        << std::isinf(inf) << '\n'
        << "isinf(0.0) = " 
        << std::isinf(0.0) << '\n'
        << "isinf(exp(800)) = " 
        << std::isinf(std::exp(800)) << '\n'
        << "isinf(DBL_MIN/2.0) = " 
        << std::isinf(DBL_MIN / 2.0) << '\n';
}

Possible Result

isinf(NaN) = false
isinf(Inf) = true
isinf(max) = false
isinf(inf) = true
isinf(0.0) = false
isinf(exp(800)) = true
isinf(DBL_MIN/2.0) = false