Dear Sirs,
I use gcc 3.4.5 and received following incorrect result in the program.
On the gcc site exist report about incorrect behavior of ++ operator but not
this situation. I hope that it will be usefull.
I have developed some stupid code to show the problem:
#include <stdio.h>
void upcase(char* str) {
size_t len;
len = strlen(str);
while(len-- > 0 )
*str++ = toupper(*str);
}
int main(int argc, char** argv) {
char buf[1000];
scanf("%s",&buf);
upcase(buf);
printf("\n%s",buf);
}
Compile: gcc -o test.exe -O2 tcode.c
Problem:
Without optimization such chunk of code is working fine, but with O2
optimization,
I have incorrect result due to gcc incremented esi earlier than read data and
as
the result - the first letter is lost.
-------- DISASM -------------
mov ebx, esi
inc esi
movsx eax, byte ptr [esi]
mov [esp+18h+var_18], eax
call toupper
mov [ebx], al
-------- DISASM -------------
Best Regards,
crow16384
