otherwise requested by the programmer, be aligned on a pre-determined boundary. The following typical alignments are valid for compilers from Microsoft (Visual C++), Borland/CodeGear (C++Builder), Digital Mars (DMC), and GNU (GCC) when compiling for 32-bit x86: A char (one byte) will be 1-byte aligned. A short (two bytes) will be 2-byte aligned. An int (four bytes) will be 4-byte aligned. A long (four bytes) will be 4-byte aligned. A float (four bytes) will be 4-byte aligned. A double (eight bytes) will be 8-byte aligned on Windows and 4-byte aligned on Linux (8-byte with -malign-double compile time option). A long long (eight bytes) will be 8-byte aligned on Windows and 4-byte aligned on Linux (8-byte with -malign-double compile time option). A long double (ten bytes with C++Builder and DMC, eight bytes with Visual C++, twelve bytes with GCC) will be 8-byte aligned with C++Builder, 2-byte aligned with DMC, 8-byte aligned with Visual C++, and 4-byte aligned with GCC. Any pointer (four bytes) will be 4-byte aligned. (e.g.: char*, int*) The only notable differences in alignment for an LP64 64-bit system when compared to a 32-bit system are: A long (eight bytes) will be 8-byte aligned. A double (eight bytes) will be 8-byte aligned. A long long (eight bytes) will be 8-byte aligned. A long double (eight bytes with Visual C++, sixteen bytes with GCC) will be 8-byte aligned with Visual C++ and 16-byte aligned with GCC. Any pointer (eight bytes) will be 8-byte aligned. Some data types are dependent on the implementation. Here is a structure with members of various types, totaling 8 bytes before compilation: struct MixedData { char Data1; short Data2; int Data3; char Data4; }; After compilation the data structure will be supplemented with padding bytes to ensure a proper alignment for each of its members: struct MixedData /* After compilation in 32-bit x86 machine */ { char Data1; /* 1 byte */ char Padding1[1]; /* 1 byte for the following 'short' to be aligned on a 2 byte boundary assuming that the address where structure begins is an even number */ short Data2; /* 2 bytes */ int Data3; /* 4 bytes - largest structure member */ char Data4; /* 1 byte */ char Padding2[3]; /* 3 bytes to make total size of the structure 12 bytes */ }; The compiled size of the structure is now 12 bytes. It is important to note that the last