NAME

strncat - append non-null bytes from a source array to a string, and null-terminate the result

LIBRARY

Standard C library (libc, -lc)

SYNOPSIS

#include <string.h>

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.

An implementation of this function might be:

char *
strncat(char *restrict dst, const char *restrict src, size_t ssize)
{

    #define strnul(s)  (s + strlen(s))

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

    return dst;
}

RETURN VALUE

strncat() returns dst.

ATTRIBUTES

For an explanation of the terms used in this section, see attributes(7).

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).

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).

BUGS

This function can be very inefficient. Read about Shlemiel the painter.

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);
}

SEE ALSO

string(3), string_copying(7)