NAME
strncat —
concatenate a string with part of
another
SYNOPSIS
#include
<string.h>
char *
strncat(char
*dst, const char
*append, size_t
count);
DESCRIPTION
The
strncat()
function appends not more than count characters of the
string append to the end of the string found in the
buffer dst. Space for the terminating
‘\0’ should not be included in
count.
Bounds checking must be performed manually with great care. If the buffer dst is not large enough to hold the result, subsequent memory will be damaged.
RETURN VALUES
The strncat() function returns the pointer
dst.
EXAMPLES
The following example shows how to use
strncat() in conjunction with
strncpy(3):
char buf[BUFSIZ]; char *base, *suffix; (void)strncpy(buf, base, sizeof(buf) - 1); buf[sizeof(buf) - 1] = '\0'; (void)strncat(buf, suffix, sizeof(buf) - 1 - strlen(buf));
The above will copy as many characters from base to buf as will fit. It then appends as many characters from suffix as will fit. If either base or suffix are too large, truncation will occur without detection.
The above example shows dangerous coding patterns, including an
inability to detect truncation. strncat() and
strncpy() are dangerously easy to misuse. The
strlcpy(3) and strlcat(3) functions are safer for this kind of
operation:
if (strlcpy(buf, base, sizeof(buf)) >= sizeof(buf) ||
strlcat(buf, suffix, sizeof(buf)) >= sizeof(buf))
goto toolong;
if (snprintf(buf, sizeof(buf), "%s%s",
base, suffix) >= sizeof(buf))
goto toolong;
SEE ALSO
STANDARDS
The strncat() function conforms to
ANSI X3.159-1989
(“ANSI C89”).
HISTORY
The strncat() function first appeared in
Version 7 AT&T UNIX.