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- Dictionarypacked/pakt/
adjective
- 1. (of a room, building, or other place) filled by a large number of people; very crowded: "a packed Merseyside pub"
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Technically, you could do all of that in one header: #ifndef PACKED / #define PACKED / #else /* !PACKED */ / #undef PACKED / #endif /* PACKED */ and then include the same header twice, once to enable and once to disable. The usefulness / cleanliness / sanity of such a practice is debatable, but so is the practice you suggest.
1. When packed used during structure declaration, compiler will not add any padding to the members of the same structure. Below is the example code and output which is self explanatory. $ cat structure_packed.c. #include <stdio.h>. typedef struct __attribute__((__packed__)) {. char a; int ai;
Aug 29, 2014 · The gcc has introduced the __attribute__((packed)) precisely to avoid the dangerous effects you are seeking: the definition of the structure should binary compatible between all the user applications and libraries which use the same definition. But the gcc also provides a way to do the packing the old fashioned, dangerous way - #pragma pack ...
6. Padding and packing are just two aspects of the same thing: packing or alignment is the size to which each member is rounded off. padding is the extra space added to match the alignment. In mystruct_A, assuming a default alignment of 4, each member is aligned on a multiple of 4 bytes.
Aug 2, 2012 · 119. packed means it will use the smallest possible space for struct Ball - i.e. it will cram fields together without padding. aligned means each struct Ball will begin on a 4 byte boundary - i.e. for any struct Ball, its address can be divided by 4. These are GCC extensions, not part of any C standard.
Apr 14, 2015 · The standard offers one extra alternative for writing pragmas: the _Pragma operator: #define PACKED_BEGIN _Pragma("pack(push, 1)") #define PACKED. #define PACKED_END _Pragma("pack(pop)") If the Borland compiler supports it, it should work. answered Apr 14, 2015 at 15:09. Angew is no longer proud of SO.
Jan 12, 2021 · IDK why that's called "unpack". – Peter Cordes. Oct 30, 2020 at 1:34. packed as in "packed together in a single register". extended packed seems to mean "extended to work with packed integers". "unpacked" is, IDK, maybe working with just the scalar or considering the register as a whole. – Margaret Bloom.
Mar 10, 2022 · 1. One effect (there are others) of applying the the packed attribute to a union is to remove any padding added at the end of the union. Here is a contrived example: #include <stdio.h>. typedef union carr {. char a[3]; short b; } Carr; typedef union __attribute__((packed)) parr {.
However, newest Xcode uses LLVM and does not recognize the attribute. How to define packed struct for LLVM? The full description of the problem might be found here. UPDATE I'm using Xcode 4.5.1 for iOS which uses Apple LLVM 4.1 compiler. I'm getting "'packed' attribute ignored" warning in Xcode in the code example above.
@DanielSantos: A quality compiler I use (Keil) recognizes "packed" qualifiers for pointers; if a structure is declared "packed", taking the address of a uint32_t member will yield a uint32_t packed*; trying to read from such a pointer on e.g. a Cortex-M0 will IIRC call a subroutine which will take ~7x as long as a normal read if the pointer is unaligned or ~3x as long if it's aligned, but will behave predictably in either case [in-line code would take 5x as long whether aligned or unaligned].
