Timeline for Would a structure ever require padding beyond what is required to align the members?
Current License: CC BY-SA 4.0
6 events
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| Sep 14, 2023 at 4:34 | comment | added | Nate Eldredge |
"Some implementations might wish to have all struct fields in the order they're declared": The C standard effectively requires this; 6.7.2.1p15 says the addresses of struct members must increase in the order in which they are declared.
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| Sep 9, 2023 at 9:47 | comment | added | kaya3 | @Barmar No ─ for example, a value sized 1 byte would be aligned at any address, whereas a 4-byte-sized value would be aligned at addresses which are a multiple of 4. Otherwise you would not be able to store an array compactly and take a pointer to one of its elements. So for example a struct of two 32-bit ints on a 64-bit machine would only require 8 bytes to properly align both fields, but would require 16 bytes if either or both fields require atomic accesses which can't be done at the sub-word level on a given machine. | |
| Sep 8, 2023 at 21:25 | comment | added | Barmar | "the target architecture only supports atomic accesses of whole words." Isn't that padding implied by "requires to ensure that all of the members are properly aligned"? | |
| Sep 8, 2023 at 21:24 | comment | added | Barmar | If you need compatibility with some specification, you usually do that by declaring explicit members for those extra spaces. | |
| Jun 14, 2023 at 15:03 | history | edited | kaya3 | CC BY-SA 4.0 |
added 206 characters in body
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| Jun 13, 2023 at 19:56 | history | answered | kaya3 | CC BY-SA 4.0 |