std::memcmp() in C++

memcmp() function compares the first count bytes ( given number of characters ) of the memory pointed to by buf1 and buf2. memcmp() is a Standard Library function defined in <string.h> header file in C++.

Syntax

int memcmp(const void *buf1, const void *buf2, size_t count);

Parameters

• buf1: Pointer to block of a memory buffer that will be compared with a second memory buffer.
• buf2: Pointer to the second block of memory buffer.
• count: Maximum numbers of bytes to compare.

Return Values

• It returns 0 when buf1 is equal to buf2.
• It returns an integer value less than zero when the first different byte in both memory buffers is less in buf1 than buf2.
• It returns an integer value greater than zero when the first different byte that is different in both memory buffers is greater in buf1 than buf2.

Note: The memcmp function does not look for ‘\0’ NULL character in the string. It will keep comparing the bytes till the specified count.

Examples of memcmp()

Example 1

The following C++ program illustrates the use of memcmp() function when buf1 is greater than buf2.

C++

// CPP program to illustrate std::memcmp()
#include <cstring>
#include <iostream>
using namespace std;

int main()
{
    // defining two buffers to compare
    char buff1[] = "Welcome to GeeksforGeeks";
    char buff2[] = "Hello Geeks ";

    int a;

    // using memcmp()
    a = memcmp(buff1, buff2, sizeof(buff1));

    // printing results
    if (a > 0)
        cout << buff1 << " is greater than " << buff2;
    else if (a < 0)
        cout << buff1 << "is less than " << buff2;
    else
        cout << buff1 << " is the same as " << buff2;

    return 0;
}

Output

Welcome to GeeksforGeeks is greater than Hello Geeks 

Example 2

The following C++ program illustrates the use of memcmp() function when buf1 is less than buf2.

C++

// CPP program to illustrate std::memcmp()
#include <cstring>
#include <iostream>
using namespace std;

int main()
{
    // comparing two strings directly
    int comp = memcmp("GEEKSFORGEEKS", "geeksforgeeks", 6);

    // result output
    if (comp == 0) {
        cout << "both are equal";
    }
    else if (comp < 0) {
        cout << "String 1 is less than String 2";
    }
    else {
        cout << "String 1 is greater than String 2";
    }
}

Output

String 1 is less than String 2

Example 3

The following C++ program illustrates the use of memcmp() function when buf1 is equal to buf2.

C++

// CPP program to illustrate std::memcmp()
#include <cstring>
#include <iostream>
using namespace std;

int main()
{
    // two buffers
    char buff1[] = "Welcome to GeeksforGeeks";
    char buff2[] = "Welcome to GeeksforGeeks";

    int a;

    // defining count using sizeof operator
    a = memcmp(buff1, buff2, sizeof(buff1));

    if (a > 0)
        cout << buff1 << " is greater than " << buff2;
    else if (a < 0)
        cout << buff1 << "is less than " << buff2;
    else
        cout << buff1 << " is the same as " << buff2;

    return 0;
}

Output

Welcome to GeeksforGeeks is the same as Welcome to GeeksforGeeks

This article is contributed by Shivani Ghughtyal. If you like GeeksforGeeks and would like to contribute, you can also write an article using contribute.geeksforgeeks.org or mail your article to contribute@geeksforgeeks.org. See your article appearing on the GeeksforGeeks main page and help other Geeks. Please write comments if you find anything incorrect, or you want to share more information about the topic discussed above.