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Thread: How to create in memory QFile

  1. #1
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    Default How to create in memory QFile

    Hi,
    I want to create a QFile that currently resides in memory. This is required as i want to add it as a resource to a QTextDocument.
    On some user action i want to write the QTextDocument and in the same directory i also want the QFile created in memory to be written.
    Please provide some pointers.

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    Default Re: How to create in memory QFile

    Ok. For that, i think dont add the file in the resource folder,except that, directly create it in your project folder and access it from there. Because if you put your file in the resource and it will get compile and you'll not able to edit it. For that,

    Qt Code:
    1. QFile *file;
    2. file=new QFile("demo.txt");.
    3. if (!file->open(QIODevice::WriteOnly | QIODevice::Text))
    4. return;
    5.  
    6. QTextStream out(file);
    7. out << "The magic number is: " << 49 << "\n";
    8.  
    9. file->close(); //for closing the file.
    To copy to clipboard, switch view to plain text mode 
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    Default Re: How to create in memory QFile

    Quote Originally Posted by sonulohani View Post
    Ok. For that, i think dont add the file in the resource folder,except that, directly create it in your project folder and access it from there. Because if you put your file in the resource and it will get compile and you'll not able to edit it. For that,

    Qt Code:
    1. QFile *file;
    2. file=new QFile("demo.txt");.
    3. if (!file->open(QIODevice::WriteOnly | QIODevice::Text))
    4. return;
    5.  
    6. QTextStream out(file);
    7. out << "The magic number is: " << 49 << "\n";
    8.  
    9. file->close(); //for closing the file.
    To copy to clipboard, switch view to plain text mode 
    contains leaks...

    Why put QFile on the heap at all?

    If op wants to write/print QTextDocument, then he should familiarise himself with http://doc.qt.io/qt-4.8/qtextdocumentwriter
    Last edited by amleto; 2nd August 2012 at 13:37.
    If you have a problem, CUT and PASTE your code. Do not retype or simplify it. Give a COMPLETE and COMPILABLE example of your problem. Otherwise we are all guessing the problem from a fabrication where relevant details are often missing.

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    Default Re: How to create in memory QFile

    I am using QTextDocumentWriter to write my QTextDocument, but here along with the document i want to write a file and add a link to the file in the document. I have added the link and it is working, but i want to write the document or not depends on whether user does export. For that I want to add the file to the document resource using the QTextDocument::addResource which will hold the QFile so that i could get the file when i want to write it.

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    Default Re: How to create in memory QFile

    QFile doesnt actually hold the data of the file so not sure that will help you much. You might as well just be saving the file name...
    If you have a problem, CUT and PASTE your code. Do not retype or simplify it. Give a COMPLETE and COMPILABLE example of your problem. Otherwise we are all guessing the problem from a fabrication where relevant details are often missing.

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    Default Re: How to create in memory QFile

    Quote Originally Posted by sonulohani View Post
    Ok. For that, i think dont add the file in the resource folder,except that, directly create it in your project folder and access it from there. Because if you put your file in the resource and it will get compile and you'll not able to edit it. For that,

    Qt Code:
    1. QFile *file;
    2. file=new QFile("demo.txt");.
    3. if (!file->open(QIODevice::WriteOnly | QIODevice::Text))
    4. return;
    5.  
    6. QTextStream out(file);
    7. out << "The magic number is: " << 49 << "\n";
    8.  
    9. file->close(); //for closing the file.
    To copy to clipboard, switch view to plain text mode 
    Qt Code:
    1. file->flush();
    To copy to clipboard, switch view to plain text mode 
    flush is very important when you write to the file Sometime can bad things happen when you don't flush it

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    Default Re: How to create in memory QFile

    Who said that QFile should always be on stack? Its depend on you whether you want to allocate in stack or heap.
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    Default Re: How to create in memory QFile

    QBuffer is the in-memory QIODevice you might want.

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    Default Re: How to create in memory QFile

    Quote Originally Posted by sonulohani View Post
    Who said that QFile should always be on stack? Its depend on you whether you want to allocate in stack or heap.
    nobody said that.

    If, however, you are going to write an example that looks like a java programmer wrote it, perhaps you should expect some comeback.
    If you have a problem, CUT and PASTE your code. Do not retype or simplify it. Give a COMPLETE and COMPILABLE example of your problem. Otherwise we are all guessing the problem from a fabrication where relevant details are often missing.

  10. #10
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    Default Re: How to create in memory QFile

    Then do coding in java, why r u here? Its depend on your program methodology. And if someone is here than atleast he should know the basic concept of c++(memory allocation). You shouldnt have to think about what they do with this code or if he /she will understand this code or not. Okay, point out the line that is causing memory leak in my code.
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    Default Re: How to create in memory QFile

    Quote Originally Posted by sonulohani View Post
    Okay, point out the line that is causing memory leak in my code.
    Qt Code:
    1. ...
    2. if (!file->open(QIODevice::WriteOnly | QIODevice::Text))
    3. return; //memoy leak if a file can't be opened
    4. ...
    To copy to clipboard, switch view to plain text mode 
    The simplest way to fix this without using delete it's just provide a parent in QFile's ctor.
    Qt Assistant -- rocks!
    please, use tags [CODE] & [/CODE].

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    Default Re: How to create in memory QFile

    No, simplest way is to say `QFile file;`, not `QFile* file = new ...`
    If you have a problem, CUT and PASTE your code. Do not retype or simplify it. Give a COMPLETE and COMPILABLE example of your problem. Otherwise we are all guessing the problem from a fabrication where relevant details are often missing.

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    Default Re: How to create in memory QFile

    Quote Originally Posted by amleto View Post
    No, simplest way is to say `QFile file;`, not `QFile* file = new ...`
    Yup, and change all "->" to "." if you have tons of code.
    Qt Assistant -- rocks!
    please, use tags [CODE] & [/CODE].

  14. #14
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    Default Re: How to create in memory QFile

    Quote Originally Posted by sonulohani View Post
    Then do coding in java, why r u here? Its depend on your program methodology. And if someone is here than atleast he should know the basic concept of c++(memory allocation). You shouldnt have to think about what they do with this code or if he /she will understand this code or not. Okay, point out the line that is causing memory leak in my code.
    You are the one writing like java: Allocating on the heap when only a local variable is needed - check. Using new without delete - check.

    Your leak has been pointed out already, although why you couldn't see it for yourself is concerning.
    If you have a problem, CUT and PASTE your code. Do not retype or simplify it. Give a COMPLETE and COMPILABLE example of your problem. Otherwise we are all guessing the problem from a fabrication where relevant details are often missing.

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