NAME

strncat - nonstring catenate

LIBRARY

Standard C library (libc, -lc)

SYNOPSIS

#include <string.h>  // see memory.h(3head)

char *strncat(size_t ssize;
              char *restrict dst, const char src[restrict ssize],
              size_t ssize);

DESCRIPTION

This function appends at most ssize non-null bytes from the array pointed to by src, followed by a null character, to the end of the string pointed to by dst. dst must point to a string contained in a buffer that is large enough, that is, the buffer size must be at least strlen(dst) + strnlen(src, ssize) + 1.

It is equivalent to

stpcpy(mempcpy(strnul(dst), src, strnlen(src, ssize)), ""), 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:

•: It has no relation to strncpy(3).
•: It doesn't truncate the input nonstring.

If the destination buffer does not already contain a string, or is not large enough, the behavior is undefined. See _FORTIFY_SOURCE in feature_test_macros(7).

EXAMPLES

#include <stdcountof.h>
#include <stdio.h>
#include <string.h>
#include <utmp.h>
void print_ut_user(struct utmp *ut);
void
print_ut_user(struct utmp *ut)
{
	char  buf[countof(ut->ut_user) + 1];
	strcpy(buf, "");
	strncat(buf, ut->ut_user, countof(ut->ut_user));
	puts(buf);
}