converting "String___gc" simply to "string"

[mitilkhatoon]

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) {}

[swoopy]

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

[mitilkhatoon]

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

[ChaosEngine]

you can convert using the following method

String dotNetString;
std::string cppString = (const char*)Marshal::StringToHGlobalAnsi(dotNetString).ToPointer()

[swoopy]

>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:

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.

[mitilkhatoon]

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();

[swoopy]

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

[swoopy]

I think it would be something like:

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.

[ChaosEngine]

forgot to mention that you'll also need

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.

[ChaosEngine]

I think it would be something like:

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

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

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)

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.

[mitilkhatoon]

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?

[mitilkhatoon]

thanks anyways ...i figured it out

this is the right way:

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

[nvoigt]

You need to free the pointer you are getting from marshalling. Look at the post above to see how it can be done.