strcpy, strcat

Standard C library (libc, -lc)

#include <string.h>

char *strcpy(char *restrict dst, const char *restrict src);
char *strcat(char *restrict dst, const char *restrict src);

strcpy()

This function copies 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.

It is equivalent to

stpcpy(dst, src), dst
    

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.

It is equivalent to

stpcpy(strnul(dst), src), dst
    

These functions return dst.

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

C11, POSIX.1-2008.

POSIX.1-2001, C89, SVr4, 4.3BSD.

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.

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

stpcpy(3), strdup(3), string(3), wcscpy(3), string_copying(7)