C library - memset() function

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The C library memset() function of type void accepts three variable as parameters that copies the character c (an unsigned char) to the first n characters of the string pointed to, by the argument str.

This function is used to fill a contiguous block of memory with a specific value. It also converts the value of a character to unsigned character and copies it into each of first n character of the object pointed by the given string. If the n is larger than string size, it will be undefined.

Syntax

Following is the syntax of the C library memset() function −

void *memset(void *str, int c, size_t n)

Parameters

This function accepts the following parameters−

• str − This is a pointer to the block of memory to fill.

• c −

  This is a second parameter of type integer and converts it to an unsigned char before using it to fill a block of memory.

• n − This is the number of bytes to be set to the value.

Return Value

This function returns a pointer to the memory area str.

Example 1

In this example, we set the initial string using C library memset() function, and to modify the string content it has to use memset() function.

#include <stdio.h>
#include <string.h>

int main () 
{
   char str[50];

   strcpy(str, "Welcome to Tutorialspoint");
   puts(str);

   memset(str, '#', 7);
   puts(str);
   
   return(0);
}

Output

The above code produces the following result−

Welcome to Tutorialspoint
####### to Tutorialspoint

Example 2

Below the program initializes an integer array with zeroes using memset().

#include <stdio.h>
#include <string.h>

int main() {
   int arr[10];
   memset(arr, 0, sizeof(arr));

   printf("Array after memset(): ");
   for (int i = 0; i < 10; i++) {
       printf("%d ", arr[i]);
   }
   printf("\n");

   return 0;
}

Output

On execution of above code, we get the following result−

Array after memset(): 0 0 0 0 0 0 0 0 0 0 

Example 3

Here, we create a C program for intializing character array with a specific character('Z') using memset().

#include <stdio.h>
#include <string.h>

int main() {
   char str[20];
   memset(str, 'Z', 10);
   printf("String after memset(): %s\n", str);
   return 0;
}

After executing the code, we get the following result−

String after memset(): ZZZZZZZZZZ