STRCPY(3)

NAME
strcpy, strncpy - copy a string

SYNOPSIS
#include <string.h>

char *strcpy(char *dest, const char *src);

char *strncpy(char *dest, const char *src, size_t n);

DESCRIPTION
The strcpy() function copies the string pointed to by src, including the terminating null byte ('\0'), to the buffer pointed to by dest. The strings may not overlap, and the destination string dest must be large enough to receive the copy.

The strncpy() function is similar, except that at most n bytes of src are copied. Warning: If there is no null byte among the first n bytes of src, the string placed in dest will not be null terminated.

If the length of src is less than n, strncpy() pads the remainder of dest with null bytes.

A simple implementation of strncpy() might be:
char*
strncpy(char *dest, const char *src, size_t n){
    size_t i;
    for (i = 0 ; i < n && src[i] != '\0' ; i++)
        dest[i] = src[i];
    for ( ; i < n ; i++)
        dest[i] = '\0';
    return dest;
}

RETURN VALUE
The strcpy() and strncpy() functions return a pointer to the destination string dest.

CONFORMING TO
SVr4, 4.3BSD, C89, C99.

NOTES
Some programmers consider strncpy() to be inefficient and error prone. If the programmer knows (i.e., includes code to test!) that the size of dest is greater than the length of src, then strcpy() can be used. If there is no terminating null byte in the first n characters of src, strncpy() produces an unterminated string in dest. Programmers often prevent this mistake by forcing termination as follows:
strncpy(buf, str, n);
if (n > 0)
    buf[n - 1]= '\0';

BUGS
If the destination string of a strcpy() is not large enough (that is, if the programmer was stupid or lazy, and failed to check the size before copying) then anything might happen. Overflowing fixed length strings is a favorite cracker technique.

SEE ALSO
bcopy(3), memccpy(3), memcpy(3), memmove(3), wcscpy(3), wcsncpy(3)

COLOPHON
This page is part of release 2.79 of the Linux man-pages project. A description of the project, and information about reporting bugs, can be found at http://www.kernel.org/doc/man-pages/.