call an external dll method in csharp

To call a method from an external DLL in C#, you need to use Platform Invocation Services (P/Invoke) and the appropriate marshaling to convert the data types between C# and the DLL. Here are the basic steps:

1. Define the DLL method signature in C# using DllImport attribute. This attribute instructs the runtime to load the dynamic library at runtime and bind with the exported function.

main.cs
[DllImport("mydll.dll")]
public static extern int MyDLLMethod(int arg1, string arg2);
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2. Use appropriate marshaling to convert the data types between C# and the DLL. You may need to marshal data types such as string, bool, char[], struct, and pointer.

main.cs
[DllImport("user32.dll", CharSet = CharSet.Unicode)]
public static extern int MessageBox(IntPtr hWnd, string text, string caption, uint type);
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3. Call the DLL method in your C# code.

main.cs
int result = MyDLLMethod(42, "hello");
MessageBox(IntPtr.Zero, $"Result = {result}", "DLL Call Result", 0);
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