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  4. Decode QString str(R"RX(...)RX") and explain what it is
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Decode QString str(R"RX(...)RX") and explain what it is

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  • Please_Help_me_DP Offline
    Please_Help_me_DP Offline
    Please_Help_me_D
    wrote on last edited by
    #1

    Hi,

    I started to learn QRegularExpression and I needed to write something like:

    QString str("Quotes " are not allowed");
    

    but as you can see I cannot simply put quote symbol " to QString.
    But I can do it in the following way:

    QString str(R"(Quotes " are not allowed)");
    

    or:

    QString str(R"RX(Quotes " are not allowed)RX");
    

    Could someone explain what this R and RX mean in this case? How to google that?

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    • jeremy_kJ Offline
      jeremy_kJ Offline
      jeremy_k
      wrote on last edited by
      #2

      R""()"" is a C++ raw string literal. RX in the last example is used as a delimiter to avoid false detection of the end of the literal.

      https://en.cppreference.com/w/cpp/language/string_literal #6

      Asking a question about code? http://eel.is/iso-c++/testcase/

      Please_Help_me_DP 1 Reply Last reply
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      • mrjjM Offline
        mrjjM Offline
        mrjj
        Lifetime Qt Champion
        wrote on last edited by mrjj
        #3

        Hi
        As jeremy_k says it's a raw string literal which helps to avoid having to escape everything.
        Before they came along one has to write it as

            QString str("\"Quotes \" are not allowed");
        

        For regular expressions, this can fast becomes very clumsy and error-prone.

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        2
        • jeremy_kJ jeremy_k

          R""()"" is a C++ raw string literal. RX in the last example is used as a delimiter to avoid false detection of the end of the literal.

          https://en.cppreference.com/w/cpp/language/string_literal #6

          Please_Help_me_DP Offline
          Please_Help_me_DP Offline
          Please_Help_me_D
          wrote on last edited by
          #4

          @jeremy_k @mrjj thank you!

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          • SGaistS Offline
            SGaistS Offline
            SGaist
            Lifetime Qt Champion
            wrote on last edited by
            #5

            Hi,

            Just in case, Qt provides a helper tool to help you write your regexps and test them.

            Interested in AI ? www.idiap.ch
            Please read the Qt Code of Conduct - https://forum.qt.io/topic/113070/qt-code-of-conduct

            1 Reply Last reply
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