table of contents
strncat(3) | Library Functions Manual | strncat(3) |
NAME¶
strncat - concatenate a null-padded character sequence into a string
LIBRARY¶
Standard C library (libc, -lc)
SYNOPSIS¶
#include <string.h>
char *strncat(char *restrict dst, const char src[restrict .sz], size_t sz);
DESCRIPTION¶
This function catenates the input character sequence contained in a null-padded fixed-width buffer, into a string at the buffer pointed to by dst. The programmer is responsible for allocating a destination buffer large enough, that is, strlen(dst) + strnlen(src, sz) + 1.
An implementation of this function might be:
char * strncat(char *restrict dst, const char *restrict src, size_t sz) {
int len;
char *p;
len = strnlen(src, sz);
p = dst + strlen(dst);
p = mempcpy(p, src, len);
*p = '\0';
return dst; }
RETURN VALUE¶
strncat() returns dst.
ATTRIBUTES¶
For an explanation of the terms used in this section, see attributes(7).
Interface | Attribute | Value |
strncat () | Thread safety | MT-Safe |
STANDARDS¶
C11, POSIX.1-2008.
HISTORY¶
POSIX.1-2001, C89, SVr4, 4.3BSD.
CAVEATS¶
The name of this function is confusing. This function has no relation to strncpy(3).
If the destination buffer is not large enough, the behavior is undefined. See _FORTIFY_SOURCE in feature_test_macros(7).
BUGS¶
This function can be very inefficient. Read about Shlemiel the painter.
EXAMPLES¶
#include <err.h> #include <stdio.h> #include <stdlib.h> #include <string.h> #define nitems(arr) (sizeof((arr)) / sizeof((arr)[0])) int main(void) {
size_t maxsize;
// Null-padded fixed-width character sequences
char pre[4] = "pre.";
char new_post[50] = ".foo.bar";
// Strings
char post[] = ".post";
char src[] = "some_long_body.post";
char *dest;
maxsize = nitems(pre) + strlen(src) - strlen(post) +
nitems(new_post) + 1;
dest = malloc(sizeof(*dest) * maxsize);
if (dest == NULL)
err(EXIT_FAILURE, "malloc()");
dest[0] = '\0'; // There's no 'cpy' function to this 'cat'.
strncat(dest, pre, nitems(pre));
strncat(dest, src, strlen(src) - strlen(post));
strncat(dest, new_post, nitems(new_post));
puts(dest); // "pre.some_long_body.foo.bar"
free(dest);
exit(EXIT_SUCCESS); }
SEE ALSO¶
string(3), string_copying(3)
2023-03-30 | Linux man-pages 6.04 |