How To Sort With The STL Compare Function Objects In C++

Modern C++ has a great deal of features and functions designed to make the process of writing apps easier and less labor-intensive. In C++, STL Standard Template Library has many algorithms for some operations like searching, counting, and manipulation of ranges and their elements. C++ has a new feature that you can sort with std::sort Parallel STL Algorithm. C++ has function objects for performing comparisons and they can be used to sort data by std::sort Parallel STL Algorithm with an appropriate C++ Dev Tool that has a C++ compiler.

What is the std::sort algorithm in C++?

The std::sort Parallel STL algorithm sorts the elements in the range from the first member to the last member in non-descending order.

The syntax for the std::sort algorithm can be described as below,

As an ExecutionPolicy std::execution::seq is used for the sequential execution, std::execution::par is used for the parallel execution . In general, there are 3 ExecutionPolicy objects you can use here,

• std::execution::seq
• std::execution::par
• std::execution::par_unseq

What are the standard library compare function objects in C++?

The standard library compare function objects are used compare data types to be used in other algorithms like sorting algorithms. The standard library compare function objects are included in C++ <functional> library header. Thus, if you want to use them you should add this <functional> library header to your code.

std::greater

std::greater is a function object for performing comparisons from higher to lower values. Unless specialized, std::greater function object invokes operator > on type T. Here is the Syntax;

For example we can use it to sort a vector as below,

std::less

std::less is a function object for performing comparisons from lower to higher values. Unless specialized, std::less function object invokes operator < on type T. Here is the Syntax;

For example we can use it to sort a vector as below,

std::greater_equal

std::greater_equal is a function object for performing comparisons. Unless specialized, std::greater_equal function object invokes operator >= on type T. Here is the Syntax;

std::less_equal

std::less_equal is a function object for performing comparisons. Unless specialized, std::less_equal function object invokes operator <= on type T.

How do I sort with the standard library compare function objects in C++?

Sometimes we require very specific sorting techniques when we sort members of data in range. In this case we can use function objects.

Here is the Syntax for the std::sort method with a function object,

Let’s assume that we want to use std::greater function object, sort will be as below,

Is there a full example of how to sort with the standard library compare function objects in C++?

Now, let’s see how we can sort a lot of vector elements with function objects, Here is a full C++ example,

Note that, in C++, if you are using arrays, std::array is on the stack, in other words it has less memory limits than vectors.

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