Introduction to Windows API

Windows Data Types

Looking at any of the functions used above, it is noticeable that the types of the arguments are not like those known by a C programmer. For example:

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BOOL ReadFileEx(
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  [in]            HANDLE                          hFile,
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  [out, optional] LPVOID                          lpBuffer,
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  [in]            DWORD                           nNumberOfBytesToRead,
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  [in, out]       LPOVERLAPPED                    lpOverlapped,
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  [in]            LPOVERLAPPED_COMPLETION_ROUTINE lpCompletionRoutine
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);

None of HANDLE, LPVOID, DWORD or LPOVERLAPPED are common outside Windows. These are in fact either struct types defined in the Windows library or just simple aliases. To explain a few aliases:

• DWORD is the alias of unsigned long
• BYTE is the alias of unsigned char
• SIZE_T is the alias of unsigned long long
• BOOL is the alias of int
• NTSTATUS is the alias of long

There are many more than those listed above, but the point is that it is useful to become familiar with these types, and a full reference is given in 5.

Certain structs, like HANDLE, have a deeper meaning in the operating system than other structs like BYTE. In the next chapter, handles are discussed in more detail. For more on mutexes see the learn section Mutex.