What is the purpose of the usort function in PHP?

The usort function is a built-in function in PHP used for custom sorting of arrays. It takes an array and a custom comparison function as parameters, sorting the array elements based on that function.

The comparison function should return an integer value that indicates the comparison result between two elements. If the result is negative, it means the first element should be placed before the second element. If the result is positive, it means the second element should be placed before the first element. If the result is 0, it means the two elements are equal and their relative positions remain unchanged.

The usort function will rearrange the elements of an array according to the rules of the comparison function, ultimately returning the sorted array.

The usort function is commonly used in situations that require custom sorting of arrays, such as sorting by a specific field in the array or by a specified sorting rule.