std::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)
SIMD overload (since C++26)
Defined in header <simd>
template < /*math-floating-point*/ V >

constexpr typename /*deduced-simd-t*/ <V> :: mask_type

  isinf ( const V& v_num ) ;
(S) (since C++26)
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)
S) The SIMD overload performs an element-wise std::isinf on v_num.
(See math-floating-point and deduced-simd-t
(since C++26)
A) Additional overloads are provided for all integer types, which are treated as double.

Parameters

num - floating-point or integer value
v_num - a data-parallel object of std::basic_simd specialization where its element type is a floating-point type

Return value

1) true if num is infinite, false
S) A data-parallel mask object where the ith element equals true if v_num[i] is infinite or false otherwise for all i in the range [ ​0​ ,  v_num.size() )

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

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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