NAME
stpcpy, stpncpy
— copy strings
SYNOPSIS
#include
<string.h>
char *
stpcpy(char
*dst, const char
*src);
char *
stpncpy(char
*dst, const char
*src, size_t
len);
DESCRIPTION
The
stpcpy()
and stpncpy() functions copy the string
src to dst (including the
terminating ‘\0’ character).
The
stpncpy()
function copies not more than len characters into
dst, appending
‘\0’ characters if
src is less than len characters
long, and
not
terminating dst if the length of
src is greater than or equal to
len.
If the src and dst strings overlap, the behavior is undefined.
RETURN VALUES
The stpcpy() function returns a pointer to
the terminating ‘\0’ character written
into dst.
The stpncpy() function returns a pointer
to the first ‘\0’ character written
into dst, or to &dst[len] if
the length of src is greater than or equal to
len.
EXAMPLES
The most common use of stpcpy() is to
build up a string from multiple elements. The following example builds up a
pathname from directory and file components using
stpcpy():
char *dir, *file, pname[PATH_MAX];
...
if (strlen(dir) + strlen("/") + strlen(file) >= sizeof(pname))
goto toolong;
stpcpy(stpcpy(stpcpy(pname, dir), "/"), file);
However, the size check required to avoid a buffer overflow is error prone since the check can become out of sync with the code that performs the copy.
One might expect that stpncpy() could be
safely used instead, but it suffers from the same defects as
strncpy(). The example below using
stpncpy() is even more prone to error and will not
detect when truncation occurs:
char *dir, *file, pname[PATH_MAX]; char *p1, *p2; ... p1 = stpncpy(pname, dir, sizeof(pname) - 1); p2 = stpncpy(p1, "/", sizeof(pname) - 1 - (p1 - pname)); stpncpy(p2, file, sizeof(pname) - 1 - (p2 - pname)); pname[sizeof(pname) - 1] = '\0';
A safer (and simpler) approach is to use
snprintf():
char *dir, *file, pname[PATH_MAX]; int len; ... len = snprintf(pname, sizeof(pname), "%s/%s", dir, file); if (len >= sizeof(pname)) goto toolong;
In most cases, it is better to use
snprintf(), strlcpy(), or
strlcat().
SEE ALSO
STANDARDS
The stpcpy() and
stpncpy() functions conform to IEEE
Std 1003.1-2008 (“POSIX.1”).
HISTORY
The function stpcpy() first appeared in
the Lattice C AmigaDOS compiler (1986 or earlier). The function
stpncpy() first appeared in the GNU C library
version 1.07 (1993). Both functions have been available since
OpenBSD 5.1.