Microsoft KB Archive/32841

= INFO: How Bitfields Are Stored in Memory =

Article ID: 32841

Article Last Modified on 12/11/2003

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APPLIES TO


 * Microsoft Visual C++ 1.0 Professional Edition
 * Microsoft Visual C++ 1.5 Professional Edition
 * Microsoft Visual C++ 1.0 Professional Edition
 * Microsoft Visual C++ 2.0 Professional Edition
 * Microsoft Visual C++ 4.0 Standard Edition
 * Microsoft Visual C++ 5.0 Standard Edition
 * Microsoft Visual C++ 6.0 Service Pack 5

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This article was previously published under Q32841



SUMMARY
An application developed with one of the Microsoft compilers above stores bitfields from low memory to high memory. For example, consider the following declaration: struct x { unsigned field_one:3; unsigned field_two:9; unsigned field_three:5; }; Compiled with a 16-bit compiler, the above code stores field_one in bits 0- 2 of the first word, field_two in bits 3-11 of the same word, and field_three in bits 0-4 of the next word (because the field cannot fit in the remaining four bits of the first word and bit fields do not cross byte boundaries). Compiled with a 32-bit compiler, the same code stores the struct in the 17 least significant bits of a word.

Additional query words: 8.00 8.00c 9.00

Keywords: kbinfo kbcompiler KB32841

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