C++ algorithm: std::min Function Template

C++ std::min

The std::min function in C++ returns the smaller of two values or, in the case of an initializer list, the smallest element in the list. This function is used in comparisons to determine the minimum value.

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Syntax of std::min

template <class T>
const T& min(const T& a, const T& b);

template <class T, class Compare>
const T& min(const T& a, const T& b, Compare comp);

template <class T>
T min(std::initializer_list<T> ilist);

template <class T, class Compare>
T min(std::initializer_list<T> ilist, Compare comp);

Parameters of std::min

Parameter	Description
a, b	The two values to compare.
ilist	An initializer list containing values to compare.
comp (optional)	A binary comparison function that defines the comparison criteria. Defaults to <.

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Return Value of std::min

Returns the smaller of the two arguments, or the smallest element in the initializer list, based on the comparison criteria.

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Examples for std::min

Example 1: Basic Usage of std::min

This example demonstrates finding the minimum of two integers:

#include <iostream>
#include <algorithm>

int main() {
    int a = 10, b = 20;
    std::cout << "Minimum of " << a << " and " << b << " is: " << std::min(a, b) << std::endl;
    return 0;
}

Output:

Minimum of 10 and 20 is: 10

Explanation:

1. We declared two integer variables, a and b, and initialized them with the values 10 and 20 respectively.
2. The std::min function is used to find the smaller of the two values. It compares a and b and returns the smaller value.
3. The result of the comparison is printed to the console using std::cout, along with an explanatory message.
4. The program terminates successfully after displaying the result.

Example 2: Using a Custom Comparison Function for std::min

You can use a custom comparison function to define the criteria for finding the minimum:

#include <iostream>
#include <algorithm>

bool abs_compare(int a, int b) {
    return std::abs(a) < std::abs(b);
}

int main() {
    int a = -10, b = 5;
    std::cout << "Minimum by absolute value of " << a << " and " << b << " is: " << std::min(a, b, abs_compare) << std::endl;
    return 0;
}

Output:

Minimum by absolute value of -10 and 5 is: 5

Explanation:

1. We defined a custom comparison function named abs_compare. This function takes two integers as arguments and compares their absolute values using std::abs.
2. We declared two integer variables, a and b, initialized with the values -10 and 5 respectively.
3. The std::min function is used with three arguments: a, b, and the custom comparison function abs_compare. It returns the value with the smaller absolute magnitude based on the custom comparison logic.

Exception Handling in std::min

The std::min function does not throw exceptions on its own, but the comparison function passed as an argument may throw exceptions.

Example 1: Exception in Custom Comparison Function

In this example, the custom comparison function throws an exception for specific values:

#include <iostream>
#include <algorithm>
#include <stdexcept>

bool faulty_compare(int a, int b) {
    if (a == 5 || b == 5) {
        throw std::runtime_error("Comparison involving 5 is not allowed.");
    }
    return a < b;
}

int main() {
    try {
        int a = 5, b = 10;
        std::cout << "Minimum is: " << std::min(a, b, faulty_compare) << std::endl;
    } catch (const std::exception& e) {
        std::cerr << "Exception caught: " << e.what() << std::endl;
    }
    return 0;
}

Output:

Exception caught: Comparison involving 5 is not allowed.

Explanation:

1. We defined a custom comparison function named faulty_compare. This function throws a std::runtime_error if either of the integers being compared is 5. Otherwise, it compares the integers in ascending order.
2. We declared two integer variables, a and b, initialized with the values 5 and 10, respectively.
3. A try block is used to safely execute the std::min function with a, b, and the custom comparison function faulty_compare.
4. When faulty_compare encounters the value 5, it throws a std::runtime_error exception with a descriptive message.
5. The catch block captures the exception and prints the error message to the console using std::cerr.