Pass string data to C# app

Jay Madren

I have searched all over the web and tried lots and lots of suggestions/solutions, but I can't get this to work.

I am building a library (dll) in Qt (Windows) to be consumed by a C# .NET application (not my app, someone else's). I need to pass string parameters back to the calling C# app (parameter - not return type, which is boolean). In most tests I use char * on the Qt side, though I have tried a few others.

I have tried all the P/Invoke, Marshalling, IntPtr, StringBuilder, etc. suggestions on the C# side and none of them work. I have, though, been able to successfully pass a string when the function returns a string, by setting the return type in C# to an IntPtr and marshalling that to a string. But trying to pass the string as one (or more) of the parameters does not work.

What is the magic to make this work?

Christian Ehrlicher

Maybe this on so helps.

Jay Madren

@Christian-Ehrlicher
This is one of the resources I already found, but it didn't help.

KroMignon

@Jay-Madren said in Pass string data to C# app:

This is one of the resources I already found, but it didn't help.

And did you also already try this?
==> https://stackoverflow.com/a/54563197/13933646

VRonin

You can use these 2 methods to convert between QString and String^ (tested working):

QString String2QString(String^ a) {
	QString Result;
	for (int i = 0; i<a->Length; i++)
		Result += (*a)[i];
	return Result;
}
String^ QString2String(const QString& a) {
	StringBuilder^ Result = gcnew StringBuilder();
	Char Tmp;
	for (int i = 0; i<a.size(); i++) {
		Tmp = a.at(i).unicode();
		Result->Append(Tmp);
	}
	return Result->ToString();
}

Now assigning to a parameter or a return type is trivial.

P.S.
Pretty sure those methods can be optimised for performance, I just copy-pasted them from a legacy project I had

Edit:
Forgot to mention String^ comes from C++/CLI (/clr compiler option)