converting "String___gc" simply to "string"

This is a discussion on converting "String___gc" simply to "string" within the C++ Programming forums, part of the General Programming Boards category; Hi I am using windows forms c++ to write a program, i need to get some string value from the ...

  1. #1
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    Question converting "String___gc" simply to "string"

    Hi

    I am using windows forms c++ to write a program, i need to get some string value from the user and pass it to a function of another class that is part of the project. However, the type of the string that I get from the text box is String___gc and I need to pass a string to my class what should I do ?

    here is a sample code of what i want to do:

    -----in the main form i have got :


    objectClass object;

    object.run(textBox1->text);

    ---- the definition of run function in the object class is:

    void object::run(string input) {}

  2. #2
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    Is String a .NET string? Or an MFC CString? Or some other string class?

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    i think it is a .Net string...it is what ever the text in a textbox in windows forms.

  4. #4
    semi-colon generator ChaosEngine's Avatar
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    you can convert using the following method
    Code:
    String dotNetString;
    std::string cppString = (const char*)Marshal::StringToHGlobalAnsi(dotNetString).ToPointer()
    "I saw a sign that said 'Drink Canada Dry', so I started"
    -- Brendan Behan

    Free Compiler: Visual C++ 2005 Express
    If you program in C++, you need Boost. You should also know how to use the Standard Library (STL). Want to make games? After reading this, I don't like WxWidgets anymore. Want to add some scripting to your App?

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    >i think it is a .Net string
    I don't know if there is any way to go directly to a C++ string. You may have to go to a char array, then to a string. It looks like the .NET String has a function called To_Char_Array(). So you might be able to do this:
    Code:
    char *temp = gc.To_Char_Array();
    string my_string(temp);
    //Now my_string should contain the contents of gc
    EDIT: It looks like ChaosEngine has your solution.

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    i can't go to char array either !!... i tried it and i get the following:

    cannot convert from '__wchar_t __gc[]' to 'char *'

    this was the code i tried : char* ip=IPTextBox->Text->ToCharArray();

  7. #7
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    Try what ChaosEngine posted. I think To_Char_Array may convert to unicode.

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    I think it would be something like:
    Code:
    String gc = IPTextBox->Text();
    string my_string = (const char*) StringToHGlobalAnsi(gc).ToPointer());
    That first line may not be quite right. I can't quite tell from what ChaosEngine posted.

  9. #9
    semi-colon generator ChaosEngine's Avatar
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    forgot to mention that you'll also need
    Code:
    using namespace System::Runtime::InteropServices;
    at the top of your file.

    Please bear in mind that as soon as you start using .Net classs in managed C++ or C++/CLI you've basically thrown standard C++ out the window.

  10. #10
    semi-colon generator ChaosEngine's Avatar
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    Quote Originally Posted by swoopy
    I think it would be something like:
    Code:
    String gc = IPTextBox->Text();
    string my_string = (const char*) Marshall::StringToHGlobalAnsi(gc).ToPointer());
    That first line may not be quite right. I can't quite tell from what ChaosEngine posted.
    it really depends on which version of visual studio you're using. if it's vs2003 then it's
    Code:
    String* gc = textbox->get_Text();
    string my_string = (const char*) Marshall::StringToHGlobalAnsi(gc).ToPointer());
    if it's vs2005 textbox->text is a property not a method os it's
    Code:
    String^ gc = textbox->Text;
    string my_string = (const char*) Marshall::StringToHGlobalAnsi(gc).ToPointer());
    actually reading the docs again you're supposed to free the memory you get back
    so the code should be (assuming vs2005)
    Code:
    String^ gc = textbox->Text;
    IntPtr textPtr = Marshall::StringToHGlobalAnsi(gc);
    string my_string = (const char*) textPtr .ToPointer());
    Marshall::FreeHGlobal(textPtr)
    there will also be some security issues calling this.
    "I saw a sign that said 'Drink Canada Dry', so I started"
    -- Brendan Behan

    Free Compiler: Visual C++ 2005 Express
    If you program in C++, you need Boost. You should also know how to use the Standard Library (STL). Want to make games? After reading this, I don't like WxWidgets anymore. Want to add some scripting to your App?

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    ChaosEngine thanks ,,,i am using 2003 .net.. I have tried the code you mentioned with the using namespace System::Runtime::InteropServices; heading, but I get an error saying : 'Marshall' : is not a class or namespace name

    is there any library or class i should include?

  12. #12
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    thanks anyways ...i figured it out

    this is the right way:
    String* managedString = IPTextBox->get_Text();
    string ip = (const char*)(Marshal::StringToHGlobalAnsi(managedString) ).ToPointer();

  13. #13
    the hat of redundancy hat nvoigt's Avatar
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    You need to free the pointer you are getting from marshalling. Look at the post above to see how it can be done.
    hth
    -nv

    She was so Blonde, she spent 20 minutes looking at the orange juice can because it said "Concentrate."

    When in doubt, read the FAQ.
    Then ask a smart question.

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