[SOLVED] (&ret)->position inequal to ret.position?

[HugeCode]

Hi. I have simple question: is this code

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(&ret)->position

inequal to this

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ret.position

counting with 'ret' as variable allocated on stack (in function body)?

[Brendan]

Hi,

Hi. I have simple question: is this code

Code: Select all

(&ret)->position

inequal to this

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ret.position

counting with 'ret' as variable allocated on stack (in function body)?

Looks equivalent to me.


Cheers,

Brendan

[HugeCode]

I don't know why but when I have variable declared in function (main(), it's toplevel function), it shows me crazy values. If I have it as static, it's OK.

[Combuster]

In other words:
- You asked the wrong question
- You're making the ancient mistake of not initializing your local variables.
- You're silencing or otherwise not listening to your compiler warnings.

[HugeCode]

... or I found out that the code compiled as 32bit can't carry more than 4 bytes from the method.

[dozniak]

... or I found out that the code compiled as 32bit can't carry more than 4 bytes from the method.

What are you talking about.

Combuster precisely told you what your problem is.
Your comment about "when static it's ok" shows you have no idea how static variables are allocated.

Go enable all warnings and read them carefully.

[HugeCode]

I know that static variables are allocated statically, so in compilation time as data. auto variables are allocated on stack. My structure has 12bytes, but I was testing only first 4 so I thought returning is OK.

[bluemoon]

I know...

You think you know it, but you dont.
The specification does not specific where to put auto variable, it can be on register, stack, on cloud, or eliminated if it does not affect program logic.

[dozniak]

... or I found out that the code compiled as 32bit can't carry more than 4 bytes from the method.

Are you saying that this does not work? While it clearly does.

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#include <assert.h>
#include <stdint.h>
#include <stdio.h>

struct a12bytestruct {
    uint32_t a, b, c;
};

struct a12bytestruct get() {
    struct a12bytestruct ret = {0xabba,0xdead,0xbabe};
    return ret;
}

int main() {
    struct a12bytestruct some = get();
    assert(some.a == 0xabba);
    assert(some.b == 0xdead);
    assert(some.c == 0xbabe);
    printf("All OK!\n");
}

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$ clang a12byteret.c -m32 -o a12byteret
$ file a12byteret
a12byteret: Mach-O executable i386
$ ./a12byteret
All OK!

[HugeCode]

For my compiler configuration it doesn't.

[Combuster]

I think that you got yourself a compiler with the PEBKAC bug enabled. It needs manual fixing.


Hint: go read forum rules 3 and 4.

[dozniak]

For my compiler configuration it doesn't.

Proof wanted.

[HugeCode]

Currently it works, it had to be caused by my pointer mess.