C++ islessequal()

The islessequal() function compares two floating-point values and returns true if the first value is less than or equal to the second. It performs a quiet comparison, meaning it does not raise floating-point exceptions and always returns false if either value is NaN.

This function is provided by the <cmath> header and is safer than using the <= operator when working with floating-point edge cases.

Syntax

islessequal(x, y)

Parameters:

• x: The first numeric value to compare.
• y: The second numeric value to compare. Both parameters can be floating-point or integer types due to overloads.

Return value:

• Returns true if x is less than or equal to y and neither value is NaN.
• Returns false otherwise, including when either argument is NaN.

Example 1: Comparing two numeric values

In this example, islessequal() is used to compare two regular numeric values:

#include <iostream>
#include <cmath>
using namespace std;

int main() {
  double a = 4.5;
  double b = 7.2;

  cout << boolalpha;
  cout << islessequal(a, b) << endl;
  cout << islessequal(b, a) << endl;

  return 0;
}

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The output of this code is:

true
false

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Example 2: Comparison involving NaN

In this example, islessequal() safely handles a comparison involving NaN:

#include <iostream>
#include <cmath>
using namespace std;

int main() {
  double x = 5.0;
  double y = NAN;

  cout << boolalpha;
  cout << islessequal(x, y) << endl;
  cout << islessequal(y, x) << endl;

  return 0;
}

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The output of this code is:

false
false

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Codebyte Example

In this example, islessequal() is used inside a helper function to check ordering between different numeric inputs:

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Frequently Asked Questions

1. What is the equal function in C++?

C++ does not have a standalone equal() function for basic comparisons; equality is typically checked using the == operator, or with helper functions like std::equal() for ranges.

2. What is the math library function in C++?

C++ math functions such as sqrt(), pow(), sin(), and islessequal() are provided by the <cmath> header.

3. Should I use equals() or == for string compare?

In C++, strings should be compared using == when working with std::string. The equals() method does not exist in standard C++.