strcpy

[houbOS1]

Hi. I'm making the basic lib functions, but now I'm stuck on strcpy.
My code looks like

Code: Select all

void strcpy(char *s1, char *s2)
{
    while (*s++ = *s2++)
      ;
}

But when I try to copy a string to another string, it doesn't work, and when I look what's really in s1 and s2 I found that for example in s1[0] there is something with an ASCII value 20, but when I run my program again, some other thing is here, etc...

Where is the bug?
Thnx for replies

[Jef]

you have to copy bytes until it find null char (ASCIIZ)

[Combuster]

It looks like you're mixing up s and s1

[Brynet-Inc]

Standard functions like that... should probably be standards compliant

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char *strcpy(char *s1, const char *s2)
{
    char *s1_p = s1;
    while (*s1++ = *s2++)
      ;
    return s1_p;
}

Have fun.

[bluecode]

Standard functions like that... should probably be standards compliant

And when you do it standard compliant, you should actually choose the newest standard. This is the C99 function declaration:

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char *strcpy(char * restrict s1, const char * restrict s2);

Be aware that some compilers don't support C99 (fully).

[houbOS1]

Thnx, now it works

[eddyb]

you have to copy bytes until it find null char (ASCIIZ)

null asci char is '\0', i'm right?

[JamesM]

Why dont you STFW and find out?

[quok]

You shouldn't use strcpy... use strncpy instead, or even better strlcpy (from OpenBSD) as that way you'll always end up with a null terminated string.

[binutils]

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#include <u.h>
#include <libc.h>
#define	N	10000

char*
strcpy(char *s1, char *s2)
{
	char *os1;

	os1 = s1;
	while(!memccpy(s1, s2, 0, N)) {
		s1 += N;
		s2 += N;
	}
	return os1;
}

[Solar]

@ quok:

1) He is writing the standard functions. Whether or not it is wise to use strcpy() is not an issue here.

2) There are perfectly good reasons in favor of strcpy(), because sometimes the preconditions are clear.

@ binutils:

Huh... That implementation not only doesn't adhere to the current definition (const, restrict), it is also depending on a non-standard helper function (memccpy())...

[binutils]

yes it is p2001 and not c99/ISO
http://www.opengroup.org/onlinepubs/009 ... mccpy.html
http://www.schweikhardt.net/identifiers.html

--
PS: and this one is my favorite part:

Run-Time Library Reference
memccpy

This POSIX function is deprecated beginning in Visual C++ 2005. Use the ISO C++ conformant _memccpy instead.

PPS: http://www.youtube.com/watch?v=JQM0_EaJ7jk :) anti-j to j

PPPS: BTW, in plan 9, strcpy for x86 is not written in c, it is asm

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/*
 * http://plan9.bell-labs.com/sys/doc/asm.html
 * http://plan9.bell-labs.com/sources/plan9/sys/src/libc/386/strcpy.s
 */

	TEXT	strcpy(SB),$0

	MOVL	$0, AX
	MOVL	$-1, CX
	CLD
/*
 * find end of second string
 */

	MOVL	p2+4(FP), DI
	REPN;	SCASB

	MOVL	DI, BX
	SUBL	p2+4(FP), BX

/*
 * copy the memory
 */
	MOVL	p1+0(FP), DI
	MOVL	p2+4(FP), SI
/*
 * copy whole longs
 */
	MOVL	BX, CX
	SHRL	$2, CX
	REP;	MOVSL
/*
 * copy the rest, by bytes
 */
	ANDL	$3, BX
	MOVL	BX, CX
	REP;	MOVSB

	MOVL	p1+0(FP), AX
	RET