Passing Argument Into Dll Call?

In my vb.net code I want to call a dll file created by Qt4.

Now everything works fine untill and unless I pass some string argument to the function.

Here is the function in dll file:

const char* QtEngineDll::randInt(char url[])
{
QString result;
/*QTextCodec *codec = QTextCodec::codecForName("UTF-8");

[Code]....

When the function returns some constant value, say if i put result = "Abhijit" then it returns the value properly. But if I want result to return value url the it is returning some garbage values.