I think you have the Struct Member Alignment set to 4 bytes (see option under Project/Settings/c++/code generation). For the struct you have shown the total size of the struct would then be 24 bytes. As it says in MSDN: The Struct Member Alignment (/Zpn) option controls how the members of a structure are packed into memory and specifies the same packing for all structures in a module. When you specify this option, each structure member after the first is stored on either the size of the member type or n-byte boundaries (where n is 1, 2, 4, 8, or 16), whichever is smaller.