Memset in C++

Memset() is a C++ function. It copies a single character for a specified number of times to an object. It is useful for filling a number of bytes with a given value starting from a specific memory location. It is defined in <cstring> header file.

Syntax:

void* memset( void* str, int ch, size_t n);

Memset() converts the value ch to unsigned char and copies it into each of the first n characters of the object pointed to by str[]. If the object is not trivially-copyable (e.g., scalar, array, or a C-compatible struct), the behavior is undefined. If n is greater than the size of the object pointed to by str, the behavior is undefined. 

Parameters:

• str[]: Pointer to the object to copy the character.
• ch: The character to copy. It can be a character, a normal value as well a boolean value.
• n: Number of bytes to copy.

Return value:  The memset() function returns str, the pointer to the destination string. 

Time Complexity: O(N) [For traverse from begin to end of the object]
Auxiliary Space Complexity: O(1)

Example:

C++

// C++ program to demonstrate memset
#include <cstring>
#include <iostream>
using namespace std;

// Driver Code
int main()
{
    char str[] = "geeksforgeeks";
    memset(str, 't', sizeof(str));
    cout << str;
    return 0;
}

Output

tttttttttttttt

Note: We can use memset() to set all values as 0 or -1 for integral data types also. It will not work if we use it to set as other values. The reason is simple, memset works byte by byte.  

C++

// C++ Program to demonstrate that we can use memset() to
// set all values as 0 or -1 for integral data types also
#include <bits/stdc++.h>
using namespace std;

// Driver Code
int main()
{
    int a[5];

    // all elements of A are zero
    memset(a, 0, sizeof(a));
    for (int i = 0; i < 5; i++)
        cout << a[i] << " ";
    cout << endl;

    // all elements of A are -1
    memset(a, -1, sizeof(a));
    for (int i = 0; i < 5; i++)
        cout << a[i] << " ";
    cout << endl;

    // Would not work
    memset(a, 5, sizeof(a)); // WRONG
    for (int i = 0; i < 5; i++)
        cout << a[i] << " ";
}

Output

0 0 0 0 0 
-1 -1 -1 -1 -1 
84215045 84215045 84215045 84215045 84215045 

Boolean Example:

C++

// C++ Program to demonstrate that we can use memset() to
// set all values as boolean data types also
#include <bits/stdc++.h>
using namespace std;

int main()
{
    bool prime[5];
    memset(prime, true, sizeof(prime));
    // If you print without using boolalpha it will print
    // like this
    for (int i = 0; i < 5; i++)
        cout << prime[i] << " ";
    cout << "\n";
    // If you use boolalpha it will print like this
    for (int i = 0; i < 5; i++)
        cout << boolalpha << prime[i] << " ";

    return 0;
}

// This code is contributed by Susobhan Akhuli

Output

1 1 1 1 1 
true true true true true 

NOTE: For boolean the object must be of bool type for C++. Eg. bool arr[n];

Advantages of memset( ) function

1. Increase readability

The main purpose of memset() function is to transform each character of the whole string into a specific int value before passing it as an input. It is a one-line piece of code, making it highly compact and improving readability overall.

2. Reduce lines of code

The same task has been accomplished more quickly than the laborious technique by utilizing this memset() function, which just accepts input, rather than the unneeded usage of loops to assign and convert the value of each character in the string to an int value.

3. It is Faster

The same task has been accomplished quickly as opposed to the time-consuming way by using this memset() function’s input alone, which eliminates the need for needless loops to assign and convert the value of each character in the string to an int value.

4. Useful in getting rid of Misalignment Problem

The C++ memset() function aids the programmer in solving the misalignment issue. There are instances where you discover that the processor is having trouble with data alignment, which results in a programming mistake. The memcpy() and memcmp() methods in C++ are the best options in this situation.

Note: memset is an old function inherited from C. It is not very flexible when filling memory with different data types and value. The std::fill function is better alternative available in STL Algorithm libary.