INFO: How Bitfields Are Stored in Memory (32841)
The information in this article applies to:
- Microsoft Visual C++ for Windows, 16-bit edition 1.0
- Microsoft Visual C++ for Windows, 16-bit edition 1.5
- Microsoft Visual C++, 32-bit Editions 1.0
- Microsoft Visual C++, 32-bit Editions 2.0
- Microsoft Visual C++, 32-bit Editions 4.0
- Microsoft Visual C++, 32-bit Editions 5.0
- Microsoft Visual C++, 32-bit Editions 6.0
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.
| Modification Type: | Major | Last Reviewed: | 12/11/2003 |
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| Keywords: | kbCompiler kbinfo KB32841 |
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