page ,132 title strcat - concatenate (append) one string to another ;*** ;strcat.asm - contains strcat() and strcpy() routines ; ; Copyright (c) 1985-1997, Microsoft Corporation. All rights reserved. ; ;Purpose: ; STRCAT concatenates (appends) a copy of the source string to the ; end of the destination string, returning the destination string. ; ;******************************************************************************* .xlist include cruntime.inc .list page ;*** ;char *strcat(dst, src) - concatenate (append) one string to another ; ;Purpose: ; Concatenates src onto the end of dest. Assumes enough ; space in dest. ; ; Algorithm: ; char * strcat (char * dst, char * src) ; { ; char * cp = dst; ; ; while( *cp ) ; ++cp; /* Find end of dst */ ; while( *cp++ = *src++ ) ; ; /* Copy src to end of dst */ ; return( dst ); ; } ; ;Entry: ; char *dst - string to which "src" is to be appended ; const char *src - string to be appended to the end of "dst" ; ;Exit: ; The address of "dst" in EAX ; ;Uses: ; EAX, ECX ; ;Exceptions: ; ;*******************************************************************************page ;*** ;char *strcpy(dst, src) - copy one string over another ; ;Purpose: ; Copies the string src into the spot specified by ; dest; assumes enough room. ; ; Algorithm: ; char * strcpy (char * dst, char * src) ; { ; char * cp = dst; ; ; while( *cp++ = *src++ ) ; ; /* Copy src over dst */ ; return( dst ); ; } ; ;Entry: ; char * dst - string over which "src" is to be copied ; const char * src - string to be copied over "dst" ; ;Exit: ; The address of "dst" in EAX ; ;Uses: ; EAX, ECX ; ;Exceptions: ;******************************************************************************* CODESEG% public strcat, strcpy ; make both functions available strcpy proc push edi ; preserve edi mov edi,[esp+8] ; edi points to dest string jmp short copy_startstrcpy endp align 16strcat proc .FPO ( 0, 2, 0, 0, 0, 0 ) mov ecx,[esp+4] ; ecx -> dest string push edi ; preserve edi test ecx,3 ; test if string is aligned on 32 bits je short find_end_of_dest_string_loopdest_misaligned: ; simple byte loop until string is aligned mov al,byte ptr [ecx] inc ecx test al,al je short start_byte_3 test ecx,3 jne short dest_misaligned align 4find_end_of_dest_string_loop: mov eax,dword ptr [ecx] ; read 4 bytes mov edx,7efefeffh add edx,eax xor eax,-1 xor eax,edx add ecx,4 test eax,81010100h je short find_end_of_dest_string_loop ; found zero byte in the loop mov eax,[ecx - 4] test al,al ; is it byte 0 je short start_byte_0 test ah,ah ; is it byte 1 je short start_byte_1 test eax,00ff0000h ; is it byte 2 je short start_byte_2 test eax,0ff000000h ; is it byte 3 je short start_byte_3 jmp short find_end_of_dest_string_loop ; taken if bits 24-30 are clear and bit ; 31 is set start_byte_3: lea edi,[ecx - 1] jmp short copy_start start_byte_2: lea edi,[ecx - 2] jmp short copy_start start_byte_1: lea edi,[ecx - 3] jmp short copy_start start_byte_0: lea edi,[ecx - 4] ; jmp short copy_start; edi points to the end of dest string. copy_start:: mov ecx,[esp+0ch] ; ecx -> sorc string test ecx,3 ; test if string is aligned on 32 bits je short main_loop_entrancesrc_misaligned: ; simple byte loop until string is aligned mov dl,byte ptr [ecx] inc ecx test dl,dl je short byte_0 mov [edi],dl inc edi test ecx,3 jne short src_misaligned jmp short main_loop_entrancemain_loop: ; edx contains first dword of sorc string mov [edi],edx ; store one more dword add edi,4 ; kick dest pointer main_loop_entrance: mov edx,7efefeffh mov eax,dword ptr [ecx] ; read 4 bytes add edx,eax xor eax,-1 xor eax,edx mov edx,[ecx] ; it's in cache now add ecx,4 ; kick dest pointer test eax,81010100h je short main_loop ; found zero byte in the loop ; main_loop_end: test dl,dl ; is it byte 0 je short byte_0 test dh,dh ; is it byte 1 je short byte_1 test edx,00ff0000h ; is it byte 2 je short byte_2 test edx,0ff000000h ; is it byte 3 je short byte_3 jmp short main_loop ; taken if bits 24-30 are clear and bit ; 31 is set byte_3: mov [edi],edx mov eax,[esp+8] ; return in eax pointer to dest string pop edi ret byte_2: mov [edi],dx mov eax,[esp+8] ; return in eax pointer to dest string mov byte ptr [edi+2],0 pop edi ret byte_1: mov [edi],dx mov eax,[esp+8] ; return in eax pointer to dest string pop edi ret byte_0: mov [edi],dl mov eax,[esp+8] ; return in eax pointer to dest string pop edi retstrcat endp end
void str_cpy(char* dest,const char* source)
{
while(*dest++=*source++);
}
stl模板库中也有定义
和zzqzzq(zzq)类似
看一看好处多多呀linux很难找的,主要是我对它不熟悉,而且现在我自己的电脑也没有用(原因太多,这里不方便说了),所以现在linux环境是找不到的,没法看大家再帮个忙,看能不能有其它办法,谢谢了先!
{
char * cp = dst; while( *cp++ = *src++ )
; /* Copy src over dst */ return( dst );
}
我搜索strcat*,没有找到一个文件
我只是知道strcpy可以copy一个string
但不知道为什么还要返回值,按照楼上热心朋友说的返回值的原因,有道理,但我感觉这不够充分用F11跟进strcpy函数?撒,不能跟进,一用F11就说找不到***.asm文件,要求自己定位,当然我也找不到了,搜索了几遍都搜不出来呀,那就是根本不存在这个文件了kao,看来是看不到这个函数的源代码了,郁闷呀
dll里边声明和现实部分都有
title strcat - concatenate (append) one string to another
;***
;strcat.asm - contains strcat() and strcpy() routines
;
; Copyright (c) 1985-1997, Microsoft Corporation. All rights reserved.
;
;Purpose:
; STRCAT concatenates (appends) a copy of the source string to the
; end of the destination string, returning the destination string.
;
;******************************************************************************* .xlist
include cruntime.inc
.list
page
;***
;char *strcat(dst, src) - concatenate (append) one string to another
;
;Purpose:
; Concatenates src onto the end of dest. Assumes enough
; space in dest.
;
; Algorithm:
; char * strcat (char * dst, char * src)
; {
; char * cp = dst;
;
; while( *cp )
; ++cp; /* Find end of dst */
; while( *cp++ = *src++ )
; ; /* Copy src to end of dst */
; return( dst );
; }
;
;Entry:
; char *dst - string to which "src" is to be appended
; const char *src - string to be appended to the end of "dst"
;
;Exit:
; The address of "dst" in EAX
;
;Uses:
; EAX, ECX
;
;Exceptions:
;
;*******************************************************************************page
;***
;char *strcpy(dst, src) - copy one string over another
;
;Purpose:
; Copies the string src into the spot specified by
; dest; assumes enough room.
;
; Algorithm:
; char * strcpy (char * dst, char * src)
; {
; char * cp = dst;
;
; while( *cp++ = *src++ )
; ; /* Copy src over dst */
; return( dst );
; }
;
;Entry:
; char * dst - string over which "src" is to be copied
; const char * src - string to be copied over "dst"
;
;Exit:
; The address of "dst" in EAX
;
;Uses:
; EAX, ECX
;
;Exceptions:
;*******************************************************************************
CODESEG% public strcat, strcpy ; make both functions available
strcpy proc
push edi ; preserve edi
mov edi,[esp+8] ; edi points to dest string
jmp short copy_startstrcpy endp align 16strcat proc .FPO ( 0, 2, 0, 0, 0, 0 ) mov ecx,[esp+4] ; ecx -> dest string
push edi ; preserve edi
test ecx,3 ; test if string is aligned on 32 bits
je short find_end_of_dest_string_loopdest_misaligned: ; simple byte loop until string is aligned
mov al,byte ptr [ecx]
inc ecx
test al,al
je short start_byte_3
test ecx,3
jne short dest_misaligned align 4find_end_of_dest_string_loop:
mov eax,dword ptr [ecx] ; read 4 bytes
mov edx,7efefeffh
add edx,eax
xor eax,-1
xor eax,edx
add ecx,4
test eax,81010100h
je short find_end_of_dest_string_loop
; found zero byte in the loop
mov eax,[ecx - 4]
test al,al ; is it byte 0
je short start_byte_0
test ah,ah ; is it byte 1
je short start_byte_1
test eax,00ff0000h ; is it byte 2
je short start_byte_2
test eax,0ff000000h ; is it byte 3
je short start_byte_3
jmp short find_end_of_dest_string_loop
; taken if bits 24-30 are clear and bit
; 31 is set
start_byte_3:
lea edi,[ecx - 1]
jmp short copy_start
start_byte_2:
lea edi,[ecx - 2]
jmp short copy_start
start_byte_1:
lea edi,[ecx - 3]
jmp short copy_start
start_byte_0:
lea edi,[ecx - 4]
; jmp short copy_start; edi points to the end of dest string.
copy_start::
mov ecx,[esp+0ch] ; ecx -> sorc string
test ecx,3 ; test if string is aligned on 32 bits
je short main_loop_entrancesrc_misaligned: ; simple byte loop until string is aligned
mov dl,byte ptr [ecx]
inc ecx
test dl,dl
je short byte_0
mov [edi],dl
inc edi
test ecx,3
jne short src_misaligned
jmp short main_loop_entrancemain_loop: ; edx contains first dword of sorc string
mov [edi],edx ; store one more dword
add edi,4 ; kick dest pointer
main_loop_entrance:
mov edx,7efefeffh
mov eax,dword ptr [ecx] ; read 4 bytes add edx,eax
xor eax,-1 xor eax,edx
mov edx,[ecx] ; it's in cache now add ecx,4 ; kick dest pointer
test eax,81010100h je short main_loop
; found zero byte in the loop
; main_loop_end:
test dl,dl ; is it byte 0
je short byte_0
test dh,dh ; is it byte 1
je short byte_1
test edx,00ff0000h ; is it byte 2
je short byte_2
test edx,0ff000000h ; is it byte 3
je short byte_3
jmp short main_loop ; taken if bits 24-30 are clear and bit
; 31 is set
byte_3:
mov [edi],edx
mov eax,[esp+8] ; return in eax pointer to dest string
pop edi
ret
byte_2:
mov [edi],dx
mov eax,[esp+8] ; return in eax pointer to dest string
mov byte ptr [edi+2],0
pop edi
ret
byte_1:
mov [edi],dx
mov eax,[esp+8] ; return in eax pointer to dest string
pop edi
ret
byte_0:
mov [edi],dl
mov eax,[esp+8] ; return in eax pointer to dest string
pop edi
retstrcat endp end
#include<string.h>
#define LPCTSTR const unsigned char*
int Istrlen(LPCTSTR lpString);
void main()
{
unsigned char st[]="12345";
LPCTSTR lpStr=st;
cout<<Istrlen(lpStr)<<endl;
}
int Istrlen(LPCTSTR lpString)
{
return strlen((char*)lpString);
}
汇编慢慢看的话,也许能懂一点点,但那太慢了,还得一边研究
也不知道到什么时候函数会结束,中间调用了什么函数
很麻烦的不知道 richardxu2002(richard) 朋友是从哪里找来的,是源码吗?
{
char *strAddr; if ((strDest == NULL) || (strSrc == NULL))
return NULL; strAddr = strDest;
while ((*strDest++ = *strSrc++) != '\0'); return strAddr;
}
如果是你这样的话,就可以改成下面这样子:会更简单一点
char *strcpy(char *strDest, const char *strSrc)
{
if ((strDest == NULL) || (strSrc == NULL))
return NULL; while ((*strDest++ = *strSrc++) != '\0'); return strDest;
}但这样做有什么意义呢?我是说返回那那个strDest有什么意义呢?有意义,但意义不大,所以根据microsoft的作风,这样是不会返回这样意义不大的值,我想,肯定是其它什么返回值和理由
又不是一个多么神秘的函数值得你去研究它的内部实现
不就是返回值嘛
当初编这函数的人也跟你一样是程序员,又不是神仙
程序员嘛,在一些无关紧要的地方可以只按照自己的喜好来编要是当时是我编的,我一时心血来潮指定他返回个BOOL甚至是个void
那以后它也就是这样了,难道你也非得找个理由出来?
run到断点的时候再按F11就可以了,我后来仔细看了一下,这段代码的注释部分就是strcpy的C实现,方法和大家说的头差不多。至于为什么要返回一个指针,我认为最大的好处在于可以实现裢式表达式比如
strlen(strcpy( pszA, pszB ) )这样的式子,其他的例子暂时想不出来,大家可以都自己去琢磨一下。其实用F11跟踪获取源码为一种很方便的方法:)