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STRCPY
Section: Linux Programmer's Manual (3)
Updated: 2010-09-20
Index
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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 (aq\0aq),
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] != aq\0aq ; i++)
dest[i] = src[i];
for ( ; i < n ; i++)
dest[i] = aq\0aq;
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]= aq\0aq;
BUGS
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.
SEE ALSO
bcopy(3),
memccpy(3),
memcpy(3),
memmove(3),
stpcpy(3),
string(3),
strdup(3),
wcscpy(3),
wcsncpy(3)
COLOPHON
This page is part of release 3.27 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/.
Index
- NAME
-
- SYNOPSIS
-
- DESCRIPTION
-
- RETURN VALUE
-
- CONFORMING TO
-
- NOTES
-
- BUGS
-
- SEE ALSO
-
- COLOPHON
-
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