NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | CONFORMING TO | NOTES | BUGS | SEE ALSO | COLOPHON
STRCPY(3) Linux Programmer's Manual STRCPY(3)
strcpy, strncpy - copy a string
#include <string.h>
char *strcpy(char *dest, const char *src);
char *strncpy(char *dest, const char *src, size_t n);
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;
}
The strcpy() and strncpy() functions return a pointer to the destination
string dest.
SVr4, 4.3BSD, C89, C99.
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';
If the destination string of a strcpy() is not large enough, then anything
might happen. Overflowing fixed-length string buffers is a favorite cracker
technique for taking complete control of the machine. Any time a program
reads or copies data into a buffer, the program first needs to check that
there's enough space. This may be unnecessary if you can show that overflow
is impossible, but be careful: programs can get changed over time, in ways
that may make the impossible possible.
bcopy(3), memccpy(3), memcpy(3), memmove(3), strdup(3), strpcpy(3), wcscpy(3),
wcsncpy(3)
This page is part of release 3.23 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/.
GNU 2009-06-01 STRCPY(3)