strcpy

Section: C Library Functions (3)
Updated: 2023-02-05
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NAME

stpcpy, strcpy, strcat - copy or catenate a string

LIBRARY

Standard C library (libc, -lc)

SYNOPSIS

#include <string.h>

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

Feature Test Macro Requirements for glibc (see feature_test_macros(7)):

stpcpy():

    Since glibc 2.10:
        _POSIX_C_SOURCE >= 200809L
    Before glibc 2.10:
        _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:

char * stpcpy(char *restrict dst, const char *restrict src) {
char *p;

p = mempcpy(dst, src, strlen(src));
*p = '\0';

return p; }

char * strcpy(char *restrict dst, const char *restrict src) {
stpcpy(dst, src);
return dst; }

char * strcat(char *restrict dst, const char *restrict src) {
stpcpy(dst + strlen(dst), src);
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() POSIX.1-2001, POSIX.1-2008, C99, 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

EXAMPLES

#include <err.h> #include <stdio.h> #include <stdlib.h> #include <string.h>

int main(void) {
    char    *p;
    char    *buf1;
    char    *buf2;
    size_t  len, maxsize;

    maxsize = strlen("Hello ") + strlen("world") + strlen("!") + 1;
    buf1 = malloc(sizeof(*buf1) * maxsize);
    if (buf1 == NULL)
        err(EXIT_FAILURE, "malloc()");
    buf2 = malloc(sizeof(*buf2) * maxsize);
    if (buf2 == NULL)
        err(EXIT_FAILURE, "malloc()");

    p = buf1;
    p = stpcpy(p, "Hello ");
    p = stpcpy(p, "world");
    p = stpcpy(p, "!");
    len = p - buf1;

    printf("[len = %zu]: ", len);
    puts(buf1);  // "Hello world!"
    free(buf1);

    strcpy(buf2, "Hello ");
    strcat(buf2, "world");
    strcat(buf2, "!");
    len = strlen(buf2);

    printf("[len = %zu]: ", len);
    puts(buf2);  // "Hello world!"
    free(buf2);

exit(EXIT_SUCCESS); }

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Time: 04:48:40 GMT, May 03, 2024