C++ Tutorial

The std::unary_negate() is a wrapper function object. It returns the opposite of the unary condition it contains. A wrapper function is a procedure in a software library or computer program that is designed to invoke a second subroutine or a system call with little or no extra processing. The function std::not1() is commonly used to create objects of type unary_negate.

Header Text:

Syntax:

It has the following syntax:

std::unary_negate<class T>
    var_name(Object of class T);

Parameters: The method std::unary_negate() takes a predicate function object as an input and returns the logical counterpart of the result produced by invoking the predicate function.

Return Value: When the predicate function is called, it returns the logical complement of the result.

The following code displays the method std::unary_negate():

Filename: UnaryNegate.cpp

// C++ program to show the use of std::unary_negate 
//to find a value larger than or equal to 6 in the array[]

#include <algorithm>
#include <functional>
#include <iostream>
#include <vector>
using namespace std;

//Predicate method for finding the number higher than 
//or equal to 4 in arrays array[]
struct con : unary_function<int, bool> {

	//The function checks the number less than 6, and if present, returns true
	bool operator()(int i)
		const
	{
		return i < 6;
	}
};


int main()
{
	// vector declaration
	vector<int> array;

	// inserting values in the vector
	for (int i = 1; i <= 10; ++i) {
		array.push_back(i);
	}

	// To obtain the count of numbers bigger than 6, use unary_negate().
	unary_negate<con> func((con()));

	//Using the method count_if(), print the value of the count.
	cout << count_if(array.begin(),
					array.end(), func);
	return 0;
}

Output:

Explanation:

The given array contains numbers from 1 to 10. From the array, the numbers that are greater than or equal to 6 are 6,7,8,9,10, so the count is 5.

Example 2:

// Program to find the number of even numbers in the array
#include < greater algorithm>
#include <functional>
#include <iostream>
#include <vector>
using namespace std;

// the struct form
struct IsOdd_cla {

	// finding the predicate value of the structure
	bool operator()(const int& x1)
		const
	{
		return x1 % 2 == 1;
	}

	typedef int argument_type;

} IsOdd_obj;

// main
int main()
{

	// Apply the unary_negate function 
	///to obtain the complement of a predicate declared in the structure 
	// IsOdd_class.
	unary_negate<IsOdd_cla>
		IsEven_obj(
			IsOdd_obj);

	// an array of elements to check the condition
	int array[] = { 1, 1, 6, 9, 5};
	int c;

	// finding according to the predicate value
	c = count_if(array, array + 5, IsEven_obj);

	// Print the count
	cout << "There were "
		<< c
		<< ?element, which was even!"
		<< endl;
	return 0;
}

Output:

There were 1 element, which was even!

Explanation:

The program constructs an IsOdd_cla structure that serves as a functor (a function object). It provides the operator() method, which determines if a given integer is odd (x1% 2 == 1). This predicate is used to distinguish between odd and even integers.

The unary_negate function is used to generate a new predicate, which is the inverse of the IsOdd_obj predicate. It serves the purpose of finding even integers by skipping the check for odd numbers.

Advantages of the Unary_negate():

There are several advantages of the unary_negate in C++. Some main advantages of the unary_negate function in C++ are as follows:

Code readability: It improves code readability and simplicity by creating the negation of a unary predicate. It eliminates the need to create a separate function for negation directly, making the code more concise and clear.
Redundant Functor Definitions Should Be Avoided: Instead of establishing a new or changing an existing functor to represent a negation, std::unary_negate generates a negated version automatically on the run, avoiding the need for additional code.
Algorithm Usage Simplicity: It combines smoothly with algorithms such as std::count_if, std::remove_if, and others, allowing for the use of negated predicates within these algorithms without the need to create additional function classes.

Next Topicstd::numeric_limits::max() and std::numeric_limits::min() in C++

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