QT app compiled in under Windows performs calculation incorrectly

I have constructed my first piece of software using QT and C++, which is working perfectly when compiled on Ubuntu 11.04 and Mac OS X. When I compile on Windows, I get strange output in my GUI. I have tracked down the problem to an error calculating the paint coordinates. This is the offending calculation:

long x = ((pos-from) *width)/range ;

        qDebug() << ***************;
        qDebug() << "pos"   <<"\t" << pos;
        qDebug() << "from"  <<"\t" << from;
        qDebug() << "width" <<"\t" << width;
        qDebug() << "range" <<"\t开发者_运维百科" << range;
        qDebug() << "x"     <<"\t" << x;
        qDebug() << "***************";

And output from Ubuntu:

        *************** 
        pos      2500000 
        from     1 
        width    1005 
        range    4411537 
        x        569 
        *************** 

And the output from Windows:

        *************** 
        pos      2500000 
        from     1 
        width    1574 
        range    4411537 
        x        -81 
        *************** 

Does anybody have an idea why I might be getting different values for x ?

Cheers.

If you are using gcc or similar (mingw) compilers, the long type is 32 bits on 32 bits platforms and 64 bits on 64 bits platforms. Probably your non-windows "compiles" are on 64 bits platforms. VC++ always considers long to be 32 bits. You can try using long long int or __int64 (older VC++) (you only need one of pos, width or range variables to be of that type so that the others are upcasted).

long type in Windows is 32-bit.

You should use long long -type if you want 64-bits len or qint64 when you use Qt.

Your width value is different in each test, so obviously the result will be different.