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How can i calculate Qstring data ?

  • i have a Qstring data like "43+40/2"
    i want to calculate it each other.. when i debug it seem "43+40/2" but i want to return it 53..

    and sometimes data could be "43+sin(30)". how can i calculate it.

  • [quote author="webadana" date="1299997503"]i have a Qstring data like "43+40/2"
    i want to calculate it each other.. when i debug it seem "43+40/2" but i want to return it 53..[/quote]

    Seems to me you need to start working on simpler problems first. QString isn't a calculator. You need to parse the string and translate it to math operations. Get the order of execution right. Lots of stuff to think about.

    Also, 43 + 40 / 2 = 63, but you probably made a typo there.

  • lol:
    43 + 40 / 2 = 63 thanks.. its very helpfull for me..:D

    i know Qstring isn't calculater and i asked how to calculate.. how can i parse ?? and order..

    may be there is a funksion to do it.. ?? is there..?

  • I would approach this using the QtScript module. Put your expression to be evaluated into a QString, add some wrapper code to create a QScriptValue from it (ie add in the function signature and curly braces). Then evaluate the resulting QScriptObject using a QScriptEngine instance.

    Something along these lines...

    QScriptEngine engine;
    QString function( myFunction() { return 43 + 40 / 2; } );

    // Tell engine about the function
    engine.evaluate( function );

    // Get a "function pointer" type object
    QScriptValue scriptFunction = engine.globalObject().property( "myFunction" );

    // Call the function
    double result =;

    Note that with this approach you can also pass arguments into the function too. See the QtScript docs for more details.

  • Indeed: QtScript is your friend. You do not want to build your own parser, I think.

    Note that the example above is missing some quotation marks on line 2...

  • Oops my bad. Thanks for pointing that out Andre.

  • if you don't think about portability, in linux you can use QProcess to execute "bc" and send to it functionString+enter
    but I am not sure if it can handle sin and cos functions

  • thank you for your answers..
    QString x = "30.5+40/2";
    QScriptEngine myEngine;
    QScriptValue x2 = myEngine.evaluate(x);
    qDebug() << x2.toNumber();
    i use this code and its work but i cant calculate sin, cos.. how can i calculate sin cos..
    i try to @ZapB 's code but it didn't calculate too.. (or i couldn't :))
    thank you very much..:)

  • @Math.sin( x )@

  • thank you but i want to calculate the x when x became like this

    @QString x = "30.5+40/2+sin(30)";@

    how can i apply on this code..

  • A hack that comes to mind is some regular expression magic. Why not simply insert the "Math." at the appropriate place in your string?

    Alternatively, you can define the functions you want to have available in your scripting environment yourself, so you don't need to modify the input string.

  • Either of the approaches suggested by Andre will work fine. Experiment and have fun.

  • one of the biggest problem I accross people dont give header when they answer to question. I spend much time to find header too. Please do not do this. Give header too in your answer. Its not Java that imports header automaticly. Its QT and C++ .

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