std:: isinf

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isinf
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Defined in header <cmath>
(1)
bool isinf ( float num ) ;

bool isinf ( double num ) ;

bool isinf ( long double num ) ;
(since C++11)
(until C++23)
constexpr bool isinf ( /* floating-point-type */ num ) ;
(since C++23)
Defined in header <cmath>
template < class Integer >
bool isinf ( Integer num ) ;
(A) (since C++11)
(constexpr since C++23)
1) 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)
A) Additional overloads are provided for all integer types, which are treated as double .

Parameters

num - floating-point or integer value

Return value

true if num is infinite, false otherwise.

Notes

GCC and Clang support a -ffinite-math option (additionally implied by -ffast-math ), which allows the respective compiler to assume the nonexistence of special IEEE-754 floating point values such as NaN, infinity, or negative zero. In other words, std::isinf is assumed to always return false under this option.

The additional overloads are not required to be provided exactly as (A) . 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 ) ) .

Example

Run this code 
#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';
}

Output: 

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

See also

(C++11)
categorizes the given floating-point value
(function)
(C++11)
checks if the given number has finite value
(function)
(C++11)
checks if the given number is NaN
(function)
(C++11)
checks if the given number is normal
(function)
C documentation for isinf
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