how to fetch a complex substring using qt?

Question

I am working my hands on QT and c++. As part of a test project, i need fetch a substring from a complex and long string, basically it is a source of a webpage. If my question looks very trivial then it would be because i am a naive qt programmer and have less experience of regular expressions.

String: "url_encoded_fmt_stream_map":"type=video%2Fwebm%3B+codecs%3D%22vp8.0%2C+vorbis%22\u0026quality=medium\u0026itag=43\u0026url=https%3A%2F%2Fr2---sn-ci5gup-qxaz.googlevideo.com%2Fvideoplayback%3Fmime%3Dvideo%252Fwebm%26key%3Dyt6%26initcwndbps%3D386250%26pcm2cms%3Dyes%26requiressl%3Dyes%26signature%3D05FB41F2F9FF5490841C7B9F40748FC4B8F505A3.0D81AB0745519F179CBF4468D2412C2240DC72F0%26ratebypass%3Dyes%26fexp%3D3300119%252C3300131%252C3313268%252C9405961%252C9416126%252C9416891%252C9419451%252C9422342%252C9422596%252C9427790%252C9428398%252C9431012%252C9433096%252C9433380%252C9433855%252C9433946%252C9434332%252C9435526%252C9435667%252C9435876%252C9436270%252C9436607%252C9436834%252C9436872%252C9436973%252C9437066%252C9437553%252C9437742%252C9438326%252C9439652%252C9439979%252C9440048%252C9440552%252C9440651%26ms%3Dau%26mt%3D1467900993%26sparams%3Ddur%252Cid%252Cinitcwndbps%252Cip%252Cipbits%252Citag%252Clmt%252Cmime%252Cmm%252Cmn%252Cms%252Cmv%252Cpcm2cms%252Cpl%252Cratebypass%252Crequiressl%252Csource%252Cupn%252Cexpire%26mv%3Dm%26ip%3D182.68.203.45%26id%3Do-AMB0Fggb71vKhXSdQqcOPdLeb9v0n2GaibsWg_W5L5b7%26mm%3D31%26mn%3Dsn-ci5gup-qxaz%26upn%3Dfri9F8GP9uA%26source%3Dyoutube%26itag%3D43%26pl%3D20%26lmt%3D1445550849945309%26expire%3D1467922869%26sver%3D3%26ipbits%3D0%26dur%3D0.000,type=video%2Fmp4%3B+codecs%3D%22avc1.42001E%2C+mp4a.40.2%22\u0026quality=medium\u0026itag=18\u0026url=https%3A%2F%2Fr2---sn-ci5gup-qxaz.googlevideo.com%2Fvideoplayback%3Fmime%3Dvideo%252Fmp4%26key%3Dyt6%26initcwndbps%3D386250%26pcm2cms%3Dyes%26requiressl%3Dyes%26signature%3D4C90C634F68098572BDCA7D5B7946F8A49A17369.D4AB7172922F499596226BA335BDF0B4519A4AC6%26ratebypass%3Dyes%26fexp%3D3300119%252C3300131%252C3313268%252C9405961%252C9416126%252C9416891%252C9419451%252C9422342%252C9422596%252C9427790%252C9428398%252C9431012%252C9433096%252C9433380%252C9433855%252C9433946%252C9434332%252C9435526%252C9435667%252C9435876%252C9436270%252C9436607%252C9436834%252C9436872%252C9436973%252C9437066%252C9437553%252C9437742%252C9438326%252C9439652%252C9439979%252C9440048%252C9440552%252C9440651%26ms%3Dau%26mt%3D1467900993%26sparams%3Ddur%252Cid%252Cinitcwndbps%252Cip%252Cipbits%252Citag%252Clmt%252Cmime%252Cmm%252Cmn%252Cms%252Cmv%252Cpcm2cms%252Cpl%252Cratebypass%252Crequiressl%252Csource%252Cupn%252Cexpire%26mv%3Dm%26ip%3D182.68.203.45%26id%3Do-AMB0Fggb71vKhXSdQqcOPdLeb9v0n2GaibsWg_W5L5b7%26mm%3D31%26mn%3Dsn-ci5gup-qxaz%26upn%3Dfri9F8GP9uA%26source%3Dyoutube%26itag%3D18%26pl%3D20%26lmt%3D1465194153116908%26expire%3D1467922869%26sver%3D3%26ipbits%3D0%26dur%3D207.354,type=video%2F3gpp%3B+codecs%3D%22mp4v.20.3%2C+mp4a.40.2%22\u0026quality=small\u0026itag=36\u0026url=

Above string is a big part of my complete string and similar pattern. This webpage source have many encoded urls which i need to seperate. below is what i am trying to seperate.

SubString:

https%3A%2F%2Fr2---sn-ci5gup-qxaz.googlevideo.com%2Fvideoplayback%3Fmime%3Dvideo%252Fwebm%26key%3Dyt6%26initcwndbps%3D386250%26pcm2cms%3Dyes%26requiressl%3Dyes%26signature%3D05FB41F2F9FF5490841C7B9F40748FC4B8F505A3.0D81AB0745519F179CBF4468D2412C2240DC72F0%26ratebypass%3Dyes%26fexp%3D3300119%252C3300131%252C3313268%252C9405961%252C9416126%252C9416891%252C9419451%252C9422342%252C9422596%252C9427790%252C9428398%252C9431012%252C9433096%252C9433380%252C9433855%252C9433946%252C9434332%252C9435526%252C9435667%252C9435876%252C9436270%252C9436607%252C9436834%252C9436872%252C9436973%252C9437066%252C9437553%252C9437742%252C9438326%252C9439652%252C9439979%252C9440048%252C9440552%252C9440651%26ms%3Dau%26mt%3D1467900993%26sparams%3Ddur%252Cid%252Cinitcwndbps%252Cip%252Cipbits%252Citag%252Clmt%252Cmime%252Cmm%252Cmn%252Cms%252Cmv%252Cpcm2cms%252Cpl%252Cratebypass%252Crequiressl%252Csource%252Cupn%252Cexpire%26mv%3Dm%26ip%3D182.68.203.45%26id%3Do-AMB0Fggb71vKhXSdQqcOPdLeb9v0n2GaibsWg_W5L5b7%26mm%3D31%26mn%3Dsn-ci5gup-qxaz%26upn%3Dfri9F8GP9uA%26source%3Dyoutube%26itag%3D43%26pl%3D20%26lmt%3D1445550849945309%26expire%3D1467922869%26sver%3D3%26ipbits%3D0%26dur%3D0.000,type=video%2Fmp4%3B+codecs%3D%22avc1.42001E%2C+mp4a.40.2%22

Please help and suggest as how can i do that using QT, C++, regular expressions. I Do not wish to use any other programming language. Thanks & Regards.

Answer 1

There is QString class for working with strings in Qt. You should study QString documentation sections: Manipulating String Data and Querying String Data. Maybe, contains() method of QString class is enough for solve your problem.

UPD:

Simple example with substring manipulating:

#include <QCoreApplication>
#include <QDebug>

int main(int argc, char *argv[])
{
    QCoreApplication a(argc, argv);

    QString bigString = "BigString BigString SubString BigString";
    QString subString = "SubString";

    bool containsFlag = bigString.contains(subString, Qt::CaseSensitive);
    int index = bigString.indexOf(subString, 0, Qt::CaseSensitive);

    qDebug() << "Length of subString: " << subString.length();
    qDebug() << "SubString contains in bigString: " << containsFlag;
    qDebug() << "SubString index in bigString: " << index;

    return a.exec();
}

As you can see, you can determine if subString contains in bigString. Of course, you can determine index of subString in bigString. You can put your own data in bigString and subString.