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std::isinf

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)
Additional overloads
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

#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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