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Marshalling Strings

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Platform invoke copies string parameters, converting them from the .NET Framework format (Unicode) to the unmanaged format (ANSI), if needed. Because managed strings are immutable, platform invoke does not copy them back from unmanaged memory to managed memory when the function returns.

The following table lists marshalling options for strings, describes their usage, and provides a link to the corresponding .NET Framework sample.

String Description Sample
By value. Passes strings as In parameters. MsgBox
As result. Returns strings from unmanaged code. Strings
By reference. Passes strings as In/Out parameters using StringBuilder. Buffers
In a structure by value. Passes strings in a structure that is an In parameter. Structs
In a structure by reference (char*). Passes strings in a structure that is an In/Out parameter. The unmanaged function expects a pointer to a character buffer and the buffer size is a member of the structure. Strings
In a structure by reference (char[]). Passes strings in a structure that is an In/Out parameter. The unmanaged function expects an embedded character buffer. OSInfo
In a class by value (char*). Passes strings in a class (a class is an In/Out parameter). The unmanaged function expects a pointer to a character buffer. OpenFileDlg
In a class by value (char[]). Passes strings in a class (a class is an In/Out parameter). The unmanaged function expects an embedded character buffer. OSInfo
As an array of strings by value. Creates an array of strings that is passed by value. Arrays
As an array of structures that contain strings by value. Creates an array of structures that contain strings and the array is passed by value. Arrays

See also