ASM Community

I tested this procedure in a dialog but my test dialog crashing after showing the result string.
Btw, this procedure may safely running in a runtime window app. What is wrong?

(using Tasm5)

StrCat  PROC  Str1:DWORD, Str2:DWORD, ResultBuff:DWORD

    USES    edi, esi

    LOCAL   Str1Len:DWORD, Str2Len:DWORD



     mov edi, Str1

     call calcLen

     mov Str1Len, ecx                   ; 1. String length

     mov edi, Str2

     call calcLen

     mov Str2Len, ecx                   ; 2. String length

     mov ecx, Str1Len



     mov esi, Str1

     mov edi, ResultBuff

     mov ecx, Str1Len

     repnz movsb                        ; ResultBuf = Str1



     mov ecx, Str2Len                   ; edi points to end of string

     mov esi, Str2                      ; esi points to 2. string

     repnz movsb                        ; ResultBuf = Str1 + Str2



     mov ecx, Str1Len

     add ecx, Str2Len

     mov byte ptr ResultBuff[ecx], 0    ; NULL terminator.



     RET



calcLen:

     mov ecx, -1

     mov al, 0

     repnz scasb

     not ecx

     dec ecx

     RETN



StrCat ENDP

;=================================================
USAGE:
.data

s1 db 'HonkiPonki',0
s2 db 'Torino',0

.data?

buffer db 100 dup(?)

.code
call StrCat, offset s1, offset s2, offset buffer
call SetDlgItemText, hwnd_, IDC_EDT1, offset buffer

cakmak,

I bet that your procedure overwrites the stack in this line:

mov byte ptr ResultBuff, 0 ; NULL terminator.

Things should work as expected if you load ResultBuff into a register first, then add ECX to that register, and store 0 where the result points to, e.g.:

mov eax, ResultBuff
mov BYTE PTR , 0

(Untested)

Regards, Frank

EDIT: instead of computing the terminator's offset, you could exploit the fact that EDI points to it anyway at this stage of the procedure :-)