'\" t
.\" Copyright 2022 Alejandro Colomar <alx@kernel.org>
.\"
.\" SPDX-License-Identifier: Linux-man-pages-copyleft
.\"
.TH strcpy 3 2023-03-30 "Linux man-pages 6.04"
.SH NAME
stpcpy, strcpy, strcat \- copy or catenate a string
.SH LIBRARY
Standard C library
.RI ( libc ", " \-lc )
.SH SYNOPSIS
.nf
.B #include <string.h>
.PP
.BI "char *stpcpy(char *restrict " dst ", const char *restrict " src );
.BI "char *strcpy(char *restrict " dst ", const char *restrict " src );
.BI "char *strcat(char *restrict " dst ", const char *restrict " src );
.fi
.PP
.RS -4
Feature Test Macro Requirements for glibc (see
.BR feature_test_macros (7)):
.RE
.PP
.BR stpcpy ():
.nf
    Since glibc 2.10:
        _POSIX_C_SOURCE >= 200809L
    Before glibc 2.10:
        _GNU_SOURCE
.fi
.SH DESCRIPTION
.TP
.BR stpcpy ()
.TQ
.BR strcpy ()
These functions copy the string pointed to by
.IR src ,
into a string
at the buffer pointed to by
.IR dst .
The programmer is responsible for allocating a destination buffer large enough,
that is,
.IR "strlen(src) + 1" .
For the difference between the two functions, see RETURN VALUE.
.TP
.BR strcat ()
This function catenates the string pointed to by
.IR src ,
after the string pointed to by
.I dst
(overwriting its terminating null byte).
The programmer is responsible for allocating a destination buffer large enough,
that is,
.IR "strlen(dst) + strlen(src) + 1" .
.PP
An implementation of these functions might be:
.PP
.in +4n
.EX
char *
stpcpy(char *restrict dst, const char *restrict src)
{
    char  *p;

    p = mempcpy(dst, src, strlen(src));
    *p = \[aq]\e0\[aq];

    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;
}
.EE
.in
.SH RETURN VALUE
.TP
.BR stpcpy ()
This function returns
a pointer to the terminating null byte of the copied string.
.TP
.BR strcpy ()
.TQ
.BR strcat ()
These functions return
.IR dst .
.SH ATTRIBUTES
For an explanation of the terms used in this section, see
.BR attributes (7).
.ad l
.nh
.TS
allbox;
lbx lb lb
l l l.
Interface	Attribute	Value
T{
.BR stpcpy (),
.BR strcpy (),
.BR strcat ()
T}	Thread safety	MT-Safe
.TE
.hy
.ad
.sp 1
.SH STANDARDS
.TP
.BR stpcpy ()
POSIX.1-2008.
.TP
.BR strcpy ()
.TQ
.BR strcat ()
C11, POSIX.1-2008.
.SH STANDARDS
.TP
.BR stpcpy ()
POSIX.1-2008.
.TP
.BR strcpy ()
.TQ
.BR strcat ()
POSIX.1-2001, C89, SVr4, 4.3BSD.
.SH CAVEATS
The strings
.I src
and
.I dst
may not overlap.
.PP
If the destination buffer is not large enough,
the behavior is undefined.
See
.B _FORTIFY_SOURCE
in
.BR feature_test_macros (7).
.PP
.BR strcat ()
can be very inefficient.
Read about
.UR https://www.joelonsoftware.com/\:2001/12/11/\:back\-to\-basics/
Shlemiel the painter
.UE .
.SH EXAMPLES
.\" SRC BEGIN (strcpy.c)
.EX
#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);
}
.EE
.\" SRC END
.SH SEE ALSO
.BR strdup (3),
.BR string (3),
.BR wcscpy (3),
.BR string_copying (7)