strcat(3) - BetterMan

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strcpy()	These functions copy the string pointed to by src, into a string at the buffer pointed to by dst. The programmer is responsible for allocating a destination buffer large enough, that is, strlen(src) + 1. For the difference between the two functions, see RETURN VALUE.
strcat()	This function catenates the string pointed to by src, after the string pointed to by dst (overwriting its terminating null byte). The programmer is responsible for allocating a destination buffer large enough, that is, strlen(dst) + strlen(src) + 1.
stpcpy()	This function returns a pointer to the terminating null byte of the copied string.
strcat()	These functions return dst.
stpcpy()	POSIX.1-2008.
strcat()	C11, POSIX.1-2008.
stpcpy()	POSIX.1-2008.
strcat()	POSIX.1-2001, C89, SVr4, 4.3BSD.

NAME

stpcpy, strcpy, strcat - copy or catenate a string

LIBRARY

Standard C library (libc, -lc)

SYNOPSIS

bash

#include <string.h>

bash

char *stpcpy(char *restrict \ndst\n, const char *restrict \nsrc\n);\n
\nchar *strcpy(char *restrict \ndst\n, const char *restrict \nsrc\n);\n
\nchar *strcat(char *restrict \ndst\n, const char *restrict \nsrc\n);

stpcpy():

bash


\n
    Since glibc 2.10:
\n
        _POSIX_C_SOURCE >= 200809L
\n
    Before glibc 2.10:
\n
        _GNU_SOURCE

DESCRIPTION

stpcpy()
strcpy(): These functions copy the string pointed to by src, into a string at the buffer pointed to by dst. The programmer is responsible for allocating a destination buffer large enough, that is, strlen(src) + 1. For the difference between the two functions, see RETURN VALUE.
strcat(): This function catenates the string pointed to by src, after the string pointed to by dst (overwriting its terminating null byte). The programmer is responsible for allocating a destination buffer large enough, that is, strlen(dst) + strlen(src) + 1.

An implementation of these functions might be:

bash

char *
stpcpy(char *restrict dst, const char *restrict src)
{
\n
    char  *p;
\n
    p = mempcpy(dst, src, strlen(src));
\n
    *p = '\0';
\n
    return p;
}
char *
strcpy(char *restrict dst, const char *restrict src)
{
\n
    stpcpy(dst, src);
\n
    return dst;
}
char *
strcat(char *restrict dst, const char *restrict src)
{
\n
    stpcpy(dst + strlen(dst), src);
\n
    return dst;
}

RETURN VALUE

stpcpy(): This function returns a pointer to the terminating null byte of the copied string.
strcpy()
strcat(): These functions return dst.

ATTRIBUTES

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

Interface	Attribute	Value
stpcpy (), strcpy (), strcat ()	Thread safety	MT-Safe

STANDARDS

stpcpy(): POSIX.1-2008.
strcpy()
strcat(): C11, POSIX.1-2008.

STANDARDS

stpcpy(): POSIX.1-2008.
strcpy()
strcat(): POSIX.1-2001, C89, SVr4, 4.3BSD.

CAVEATS

The strings src and dst may not overlap.

If the destination buffer is not large enough, the behavior is undefined. See _FORTIFY_SOURCE in feature_test_macros(7).

strcat() can be very inefficient. Read about Shlemiel the painter (opens in new tab).

EXAMPLES

bash

#include <err.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
int
main(void)
{
\n
    char    *p;
\n
    char    *buf1;
\n
    char    *buf2;
\n
    size_t  len, maxsize;
\n
    maxsize = strlen("Hello ") + strlen("world") + strlen("!") + 1;
\n
    buf1 = malloc(sizeof(*buf1) * maxsize);
\n
    if (buf1 == NULL)
\n
        err(EXIT_FAILURE, "malloc()");
\n
    buf2 = malloc(sizeof(*buf2) * maxsize);
\n
    if (buf2 == NULL)
\n
        err(EXIT_FAILURE, "malloc()");
\n
    p = buf1;
\n
    p = stpcpy(p, "Hello ");
\n
    p = stpcpy(p, "world");
\n
    p = stpcpy(p, "!");
\n
    len = p - buf1;
\n
    printf("[len = %zu]: ", len);
\n
    puts(buf1);  // "Hello world!"
\n
    free(buf1);
\n
    strcpy(buf2, "Hello ");
\n
    strcat(buf2, "world");
\n
    strcat(buf2, "!");
\n
    len = strlen(buf2);
\n
    printf("[len = %zu]: ", len);
\n
    puts(buf2);  // "Hello world!"
\n
    free(buf2);
\n
    exit(EXIT_SUCCESS);
}