Query related to C

Any one has information about following Macro.

[SIZE="5"]# Pragram Pack()[/SIZE]

#pragma pack directive modifies the current alignment rule for members of structures whose declaration following the directives. This member can't increase the alignment of a member, but rather can decrease the alignment. It is stack based. All packs are pushed into stack as the source code is parsed. The value at the top if the current pragmapack is the value used to pack members of all subsequent structures within scope of current alingment. #pragmapack directive causes bitfield to cross bitfield container boundaries

#pragma pack directive modifies the current alignment rule for members of structures whose declaration following the directives. This member can't increase the alignment of a member, but rather can decrease the alignment. It is stack based. All packs are pushed into stack as the source code is parsed. The value at the top if the current pragmapack is the value used to pack members of all subsequent structures within scope of current alingment. #pragmapack directive causes bitfield to cross bitfield container boundaries