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fpclassify() method in C/C++ with Examples

Last Updated : 12 Jul, 2025
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The fpclassify() function are defined in header math.h header in C and cmath library in C++. This function is used to get the value of type int that matches one of the classification macro constants (depending on the value of x). Syntax: 
int fpclassify(int x);
int fpclassify(float x);
int fpclassify(double x);
int fpclassify(long double x);
Parameters: This method accepts a parameter x which is the value to be matched with one of the macro constants of this method. It can be integer, float, double or long double. Return Value: This function returns integer values for the macro constants as follows:
  • FP_INFINITE: When the specified value is Positive or negative infinity
  • FP_NAN: When the specified value is not a Number
  • FP_ZERO: When the specified value is a zero.
  • FP_SUBNORMAL: When the specified value is a positive or negative denormalized value
  • FP_NORMAL: When the specified value is a positive or negative normalized non-zero value
Below example demonstrate the use of fpclassify() method: CPP 
// C++ program to demonstrate
// the use of fpclassify() method

#include <iostream>
#include <math.h>
using namespace std;

// Function to implement fpclassify() method
void fpclassification(double x)
{

    // fpclassify() method
    switch (fpclassify(x)) {

    // For the data to be infinite
    case FP_INFINITE:
        cout << "Infinite Number \n";
        break;

    // For the data to be not defined
    // as in divide by zero
    case FP_NAN:
        cout << "Not a Number \n";
        break;

    // For the data to be zero
    case FP_ZERO:
        cout << "Zero \n";
        break;

    // For the data to be subnormal
    case FP_SUBNORMAL:
        cout << "Subnormal value \n";
        break;

    // For the data to be normal
    case FP_NORMAL:
        cout << "Normal value \n";
        break;

    // For the data to be invalid
    default:
        cout << "Invalid number \n";
    }
}

// Driver code
int main()
{

    // Example 1
    double a = 1.0 / 0.0;
    cout << "For 1.0/0.0: ";
    fpclassification(a);

    // Example 2
    double b = 0.0 / 0.0;
    cout << "For 0.0/0.0: ";
    fpclassification(b);

    // Example 3
    double c = -0.0;
    cout << "For -0.0: ";
    fpclassification(c);

    // Example 4
    double d = 1.0;
    cout << "For 1.0: ";
    fpclassification(d);

    return 0;
}
Output: 
For 1.0/0.0: Infinite Number 
For 0.0/0.0: Not a Number 
For -0.0: Zero 
For 1.0: Normal value

V
verma_anushka
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