Questions tagged [packed]
78 questions
4
votes
2 answers
__attribute__((packed)) alternative
consider the following structure:
typedef struct __attribute__((packed)) a{
int a1;
int b2;
char cArray[5];
int c3;
} Mystruct;
Now in my code, Im doing this:
char source[50];
Mystruct mm;
//...
//initialization and other…
Dipto
- 2,720
- 2
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- 42
3
votes
2 answers
Using attribute packed for classes in GCC
GCC doc says:
You may only specify the packed attribute attribute on the definition
of an enum, struct or union, not on a typedef that does not also
define the enumerated type, structure or union.
Does it mean that I cannot apply this attribute…
user1641854
3
votes
4 answers
Writing 'packed' structs to file using C
How can I "pack" and "write" a struct to a file using C so that:
struct a {
uint64_t a;
char* b;
uint16_t c;
} a;
a b;
b.a = 3;
b.b = "Hello";
b.c = 4;
gets written to the file as
00 00 00 00 00 00 00 03 48 65 6c 6c 6f 00 00 04
Delan Azabani
- 79,602
- 28
- 170
- 210
3
votes
2 answers
Packing bitfields even more tightly
I have a problem with bitfields in derived classes.
With the g++ compiler, you can assign __attribute__((packed)) to a class and it will pack bitfields. So
class A
{
public:
int one:10;
int two:10;
int three:10;
} __attribute__…
Mr Lister
- 45,515
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3
votes
2 answers
Sha 1 hashes and their length with the bit torrent protocol (magnets)?
I am scraping websites for information and it involves getting sha1 hashes of magnet links.
I get all the magnet links with a simple preg_match_all but in my results I am getting weird results, I understand that a magnet hash in its hexadecimal form…
Griff
- 1,647
- 2
- 17
- 27
2
votes
1 answer
Weird result for packed number multiplication in an enhancement
I am missing a part to solve my problem.
If I do this operation :
TYPES: ty_p2 TYPE p DECIMALS 2.
DATA: lv_test TYPE ty_p2.
lv_test = '100.00' * '3.00'.
I got this result in a program (specific program) on debugger view :
this is the actual…
depth1
- 135
- 10
2
votes
2 answers
What does __attribute__((packed)) do to a union?
The spec (GCC type attributes amongst others) states that __attribute__((packed)) can be applied to a struct or a union.
Since all union fields' storage overlap, what does the attribute actually do to a union? If you have various structures in the…
Willie Visagie
- 171
- 1
- 14
2
votes
2 answers
How to properly access packed struct members
What is the correct way to access packed struct's members?
struct __attribute__ ((packed)) MyData {
char ch;
int i;
}
void g(int *x); // do something with x
void foo(MyData m) {
g(&m.i);
}
void bar(MyData m) {
int x = m.i;
…
DDG
- 147
- 1
- 6
2
votes
3 answers
ARM GCC Address of packed struct warning
In my code, I have something like this:
#include
typedef struct __attribute__((packed)) {
uint8_t test1;
uint16_t test2;
} test_struct_t;
test_struct_t test_struct;
int main(void)
{
uint32_t *ptr = (uint32_t*) &test_struct;
…
energetic
- 897
- 1
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- 7
2
votes
1 answer
Creating new objects versus encoding data in primitives
Let's assume I want to store (integer) x/y-values, what is considered more efficient: Storing it in a primitive value like long (which fits perfect, due sizeof(long) = 2*sizeof(int)) using bit-operations like shift, or and a mask, or creating a…
NHSH
- 69
- 7
2
votes
2 answers
Sizeof of packed structure with bit fields
Consider this code:
#include
#include
#ifdef __GNUC__
#define PACK( __Declaration__ ) __Declaration__ __attribute__((__packed__))
#endif
#ifdef _MSC_VER
#define PACK( __Declaration__ ) __pragma(pack(push, 1)) __Declaration__…
pmor
- 5,392
- 4
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- 36
2
votes
1 answer
How can I be sure that this C structure is packed both on 32 bit and 64 bit systems? Is "__attribute__((packed))" always necessary?
I'm trying to build a simple custom application layer protocol, essentially carrying a timestamp, plus some other useful information, in order to perform few network measurements between different Linux systems.
The implementation, in my initial…
es483
- 361
- 2
- 16
2
votes
2 answers
Fast list-product sign for PackedArray?
As a continuation of my previous question, Simon's method to find the list product of a PackedArray is fast, but it does not work with negative values.
This can be "fixed" by Abs with minimal time penalty, but the sign is lost, so I will need to…
Mr.Wizard
- 24,179
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2
votes
0 answers
How to keep packed structs member sorted by declaration order in Doxygen
I use doxygen to document a C++ codebase which uses some packed structs to represent communication buffers. I usually like the alphabetical order of members doxygen uses because it makes it easier to find something in the documentation. However, I'd…
lgeorget
- 400
- 4
- 13
2
votes
0 answers
Warning in assigning packed structure to global structure
I'm running on an (embedded) ARM architecture.
I have a structure Brown:
typedef struct
{
float A;
float B;
float C;
}Brown;
a packed structure Abo that contains Brown:
#pragma pack(2)
typedef struct
{
Brown Left;
Brown…
Yuval
- 21
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