5.00 Optimization Bug?

[Francesco]

If I switch on optimization in the IDE (Optimizations: Maximum Speed), the following (sample-)code gives unexpected results. But it seems to work fine without optimization (Optimizations: None). System: Windows 2000 (on AMD Athlon 64 Dual Core). Pelles C 5.00.

Input (say): test
Output: tst                   <---

If I replace my_getchar() with getchar() in getword() no problem shows up.

Code Select Expand


#include <stdio.h>
#include <ctype.h>

void getword(char *);

int main(void)
{
    char buffer[1000];

    getword(buffer);
    printf("%s\n", buffer);

    return 0;
}

int my_getchar(void)
{
    return getchar();
}

void getword(char *word)
{
    char *w = word;

    while (1)
    {
        *w = my_getchar();
       
        if (*w == '\n') break;

        w++;
    }
    *w = '\0';
   
    return;
}


[Pelle]

Yes, a bug: getchar() is normally a macro, and it contains a conditional operator ( ?: ) and a fetch with a post-increment (like *p++). If you put a conditional operator and a fetch with post-increment in a *return statement*, the fetch is acting like *++p, "thanks" to a new return optimization. Pity this wasn't found during beta testing; guess I should just skip that phase in the future...

Another way to "fix" this until I can upload a new version is just to undefine the getchar macro, somewhere after #include <stdio.h>:
like so:

Code Select Expand

#include <stdio.h>
#undef getchar

[Francesco]

Never mind, Pelle. I'll "test" your compiler/IDE now by (extensively) using it. 
Keep on the good work!

[Pelle]

Thanks. I have this fixed now, and will upload it later - unless you find something else...