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BSTR MethodOne (BSTR b) {
return b;
}
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However, if you define the method as a platform invoke prototype, replace each BSTR type with a String type, and call MethodOne, the common language runtime attempts to free b twice. You can change the marshaling behavior by using IntPtr types rather than String types.
The runtime always uses the CoTaskMemFree method to free memory. If the memory you are working with was not allocated with the CoTaskMemAlloc method, you must use an IntPtr and free the memory manually using the appropriate method. Similarly, you can avoid automatic memory freeing in situations where memory should never be freed, such as when using the GetCommandLine function from Kernel32.dll, which returns a pointer to kernel memory. For details on manually freeing memory, see the Buffers Sample.