DotNet - What is int*?

Question

simple question, I import a DLL function and the parameter are int*. When I try to enter Method(0), I get an error which says: \"int and int* can not convert\".

What

Answer 1

It's a pointer to an int. Generally best avoided in managed code. You might want to post your imported method declaration. An IntPtr is usually sufficient for this kind of interop.

Answer 2

That is classic C notation for a pointer to an int. Whenever a type is followed by a *, it denotes that type as a pointer to that type. In C#, unlike in C, you must explicitly define functions as unsafe to use pointers, in addition to enabling unsafe code in your project properties. A pointer type is also not directly interchangeable with a concrete type, so the reference of a type must be taken first. To get a pointer to another type, such as an int, in C# (or C & C++ for that matter), you must use the dereference operator & (ampersand) in front of the variable you wish to get a pointer to:

unsafe
{
    int i = 5;
    int* p = &i;
    // Invoke with pointer to i
    Method(p);
}

'Unsafe' code C#

Below are some key articles on unsafe code and the use of pointers in C#.

• Unsafe contexts
• Pointer Types
• Fixed and movable variables
• Pointer conversions
• Pointers in expressions
• The 'fixed' statement
• Stack allocation
• Dynamic memory allocation

Answer 3

It depends on the language you use. In C#, you should declare the argument with the "ref" keyword. In VB.NET you should use the ByRef keyword. And you need to call it by passing a variable, not a constant. Something like this:

 int retval = 0;
 Method(ref retval);
 // Do something with retval
 //...