Is there any way to force an alignment of a particular element of a struct using a GNUism?
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I am porting an application to an ARM platform in C, the application also runs on an x86 processor, and must be backward compatible.
I am now having some issues with variable ... |
I am modifying a bit of C code, that goes roughly like this:
typedef struct STRUCT_FOO {
ULONG FooInfo;
union { ...
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I have the structure
typedef struct EData
{
int a;
char c;
}
Edata obj;
a is the integer variable so it takes 4 bytes and the c is the ... |
Is there any tool that could verify the alignment of all structures in a particular set of C files and let us know the improperly packed structures so that proper packing(padding) ... |
the __alignof value is the alignment
requirement of the largest element in
the structure.
Why??
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I am working on firmware for a 16-bit PIC and writing in C (Microchip C30 compiler). My device receives a long list of bytes from an external device, and then I ... |
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I always assume, as they said here http://en.wikipedia.org/wiki/Data_structure_alignment, "It is important to note that the last member is padded with the number of bytes required so that the total ... |
Is there a way in gcc or clang (or any other compiler) to spit information about whether a struct has holes (memory alignment - wise) in it ?
Thank you.
ps: ... |
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Absolutely, C (and C++) adds padding bytes to structures so that the members in the structure are aligned onto memory boundaries that are easy for the processor to access. Generally this greatly speeds up any program (trying to read an unaligned word on a 16bit machine would typically take 2 byte reads a shift and an or as opposed to a ... |
junky_fellow@yahoo.co.in wrote: I read some notes that say that if we keep the frequently accessed structures aligned to the size of cpu cache line, then we may get improved performance. > Is anyone aware of how this alignment can help in increasing the performance ? Standard C says nothing about cache lines. |
To make it easier and faster for the processor to access the data. All processors will have a native data bus width and (normally) read data from memory aligned to this width. If, for instance, I have a 32 bit processor then it will read memory location aligned to 32 bits. If I am reading a 32 bit integer from memory ... |
struct a { int b; char a; int c; } On i386 the sizeof this structure would be 12 bytes,as 3 bytes are padded after a so that c is aligned on 4byte boundary. So the doubts that i have is 1) Does the poratbility issue come into play only when i persist this structure on one architecture ( for ex ... |
Can somebody please tell me about the structure alignment rules ? What I found was that on my system (cygwin running on PC, size of int=4 sizeof long=4, size of long long = 8) the cygwin compiler put the padding after the last member of structure. For eg, struct test { int i; char c; /* no padding required between int ... |
let say i have struct SA { long l1; long l2: long l3; }; struct SB: public SA { long l4; }; SB test; - - - - - - is is save to do the following... void* pl3 = ((long*) &test) + 2 void* pl4 = ((long*) &test) + 3 .... to get pointers to l3 and l4? i'm asking ... |
Hi. Assuming a struct: struct data{ int, a, b, c, d; }; Can I assume that the four variables from data are stored in memory in order given above? Or would it be possible that they look like this in memory: a, c, d, b? I'm using the Visual Studio 2005 Pro compiler. g, Hipo |
I create new prj w/ MSVC++ 6. This prj have compiler's option : Default struct alignment == 8 /Zp8 so i don't know how do i declare myStruct w/ no alignment (align(1)). i declared __declspec(align(1)) struct tagMAB_CODE_HEADER{ uint8 iID; uint8 iSection[8]; uint16 iLength; uint8 iCmdID; uint8 iResponse; } ; typedef struct tagMAB_CODE_HEADER MAB_CODE_HEADER; but it's not work ? nm. |
> You shouldn't need any special declarations. Just make sure that when you allocate space for the page table that the space is page aligned. That's the point of trying to align it to 4kb. I don't plan on ever enabling PAE, so I should be fine with 4kb. > Print the address (in hex), and make sure the right-most 12 ... |
> Does the long double always have the most strict alignment requirements? Probably, though I don't think it's a guarantee. IIRC, the standard only mentions that different data types can have different alignments, and the need to make sure the alignments are preserved, but doesn't go on to specify what they should be (if anything). > And does this guarantee that ... |
Greetings, How might you go about determining the alignment of a struct at runtime? I need to be able to read (at runtime) a struct definition, fill it with data, write it to a disk file - then in another program that has the structure actually defined at compile time, read the data from the disk file and populate the struct. ... |
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__________________ The essence of Christianity is told us in the Garden of Eden history. The fruit that was forbidden was on the Tree of Knowledge. The subtext is, All the suffering you have is because you wanted to find out what was going on. You could be in the Garden of Eden if you had just kept your f***ing mouth shut ... |
/* Packet received on port (datapath -> controller). */ struct ofp_packet_in { struct ofp_header header; uint32_t buffer_id; /* ID assigned by datapath. */ uint16_t total_len; /* Full length of frame. */ uint16_t in_port; /* Port on which frame was received. */ uint8_t reason; /* Reason packet is being sent (one of OFPR_*) */ uint8_t pad; uint8_t data[0]; /* Ethernet frame, halfway ... |