Sams Teach Yourself C in 21 Days

Manipulating Strings 485

17

Thestrncpy()Function ................................................................................

Thestrncpy()function is similar to strcpy(), except that strncpy()lets you specify

how many characters to copy. Its prototype is

char *strncpy(char *destination, const char *source, size_t n);

The arguments destinationandsourceare pointers to the destination and source

strings. The function copies, at most, the first ncharacters of sourcetodestination. If

sourceis shorter than ncharacters, enough null characters are added at the end of

sourceto make a total of ncharacters copied to destination. If sourceis longer than n

characters, no terminating \0is added to destination. The function’s return value is

destination.

Listing 17.3 demonstrates the use of strncpy().

LISTING17.3 strncpy.c. The strncpy()function

1: /* Using the strncpy() function. */

2:

3: #include <stdio.h>

4: #include <string.h>

5:

6: char dest[] = “..........................”;

7: char source[] = “abcdefghijklmnopqrstuvwxyz”;

8:

9: int main( void )

10: {

11: size_t n;

12:

13: while (1)

14: {

15: puts(“Enter the number of characters to copy (1-26)”);

16: scanf(“%d”, &n);

17:

18: if (n > 0 && n< 27)

19: break;

20: }

21:

22: printf(“\nBefore strncpy destination = %s”, dest);

23:

24: strncpy(dest, source, n);

25:

26: printf(“\nAfter strncpy destination = %s\n”, dest);

27: return 0;

28: }

28 448201x-CH17 8/13/02 11:13 AM Page 485