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kas1e
signed char became unsigned ?
Posted on: 2021/1/21 19:42    #1
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@All

Have some theoretical question.

I do work on some port of a game, which is C++ and which have such a class:

class Door : public Object
{
    public :
        ...balbalba...

    private :

        ...balbalba...

        char _direction;

        ...balbalba...

};



Now, in the code of the game, depending on the needs, we have set _direction to be 1 or -1. Like this:

void Door::setDirection(core::vector3df ref)
{
    if (_doorType == DT_ROTATE_X)
    {
        if (ref.Z < _rotateCenter->getPosition().Z) _direction = 1;
        else _direction = -1;
    }
    else if (_doorType == DT_ROTATE_Z)
    {
        if (ref.X < _rotateCenter->getPosition().X) _direction = -1;
        else _direction = 1;
    }
}


And when I build it for win32 and when puts prints with %d in relevant parts, it prints 1 or -1 when should.

But when I do the same on amigaos4, it prints then 1 and 255 instead of 1 and -1 (i.e. -1 became 255).

I.e. exactly the same code line per line. Just 2 binaries, one for aos4 and one for win32.

I feel it's something trivial, just can't get what. Does it look like signed char become unsigned? Maybe I need specially specify that this is signed? Or maybe some flag to GCC need to be passed, or it just bad code-practice somewhere?

Maybe in win32 pure "char" mean "signed char", but on amigaos4 pure "char" mean "unsigned char" ?:)
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kas1e
Re: signed char became unsigned ?
Posted on: 2021/1/21 20:00    #2
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Damn right, win32:

$ cat test.cpp
#include <stdio.h>
int main()
{
        char _direction;
        _direction = -1;
        printf("_direction = %d\n",_direction);
}

$ gcc test.cpp -o test
$ ./test
_direction = -1



Amigaos4:

2/10.Work:test> cat test.cpp
#include <stdio.h>
int main()
{
        char _direction;
        _direction = -1;
        printf("_direction = %d\n",_direction);
}

2/10.Work:test> gcc test.cpp -o test
2/10.Work:test> ./test
2/10.Work:test> _direction = 255


So seems just different defaults. Strange through why differences have a place at all between platforms in such case.
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salass00
Re: signed char became unsigned ?
Posted on: 2021/1/21 20:20    #3
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@kas1e

Whether char type defaults to signed or unsigned is and always has been platform dependent. If you require a specific type of char (signed or unsigned) you should specify it in the variable definition.

In this case:
signed char _direction = -1;
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Thematic
Re: signed char became unsigned ?
Posted on: 2021/1/21 20:44    #4
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There should be a warning in gcc for that. It's *the* cross platform toolchain.
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flash
Re: signed char became unsigned ?
Posted on: 2021/1/21 21:13    #5
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These is a gcc compiler option about how to manage chars datatypes.
Maybe on windows defaults are different from others platforms.
As suggested you can declare var as signed char and look at debug printf output just to verify.
Memento audere semper!
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kas1e
Re: signed char became unsigned ?
Posted on: 2021/1/21 22:03    #6
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As code is written like this, probably it's better to use --fsigned-char GCC option then? Or it may fix this part, but fail then in another...
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billyfish
Re: signed char became unsigned ?
Posted on: 2021/1/21 22:18    #7
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@kas1e

-fsigned-char should do it for you in GCC.
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