C - strncpy() function

C strncpy() function - copy fixed length string, returning a pointer to the array end

Syntax:

char *strncpy(char *string1, const char *string2, size_t n);

The strncpy() function is used to copy n characters of string2 to string1. If n is less than or equal to the length of string2, a null character (\0) is not appended to the copied string. If n is greater than the length of string2, the string1 result is padded with null characters (\0) up to length n.

Parameters:

Return value from strncpy()

• The strncpy() function returns a pointer to string1.

Example: strncpy() function

#include <stdio.h>
#include <string.h>
 
#define SIZE 40
 
int main(void)
{
  char string1[ SIZE ] = "123456789";
  char string2[ SIZE ] = "abcdefg";
  char string3[ SIZE ] = "123456789";  
  char string4[ SIZE ] = "abcdefg";
  char * return_string;
  int  n = 2; 
  printf("Original strings:");
  printf("\nString1: %s",string1);
  printf("\nString2: %s",string2);
  printf("\nn = %d",n);
  return_string = strncpy( string1, string2, n);
  printf("\nAfter strncpy(string1, string2, n):");
  printf("\nString1: %s",string1);
  printf("\nString2: %s",string2);
  n = 5; 
  printf("\n\nOriginal strings:");
  printf("\nString3: %s",string3);
  printf("\nString4: %s",string4);
  printf("\nn = %d",n);
  return_string = strncpy(string3, string4, n);
  printf("\nAfter strncpy(string3, string4, n):");
  printf("\nString3: %s",string3);
  printf("\nString4: %s",string4);
}
 

Output:

Original strings:
String1: 123456789
String2: abcdefg
n = 2
After strncpy(string1, string2, n):
String1: ab3456789
String2: abcdefg

Original strings:
String3: 123456789
String4: abcdefg
n = 5
After strncpy(string3, string4, n):
String3: abcde6789
String4: abcdefg

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