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struct ia32_gateDescriptor{
unsigned int offset_lo:16; //!< target offset (bits 0..15)
unsigned int selector:16; //!< target segment selector
int :8;
unsigned int type:5; //!< gate type
/*!< \see ia32_descrtype */
unsigned int dpl:2; //!< requested priviledge level to access
unsigned int present:1;
unsigned int offset_hi:16; //!< target offset (bits 16..31)
};
Everything i've seen so far tends to prove that on GCC, for IA-32 platforms, the 'memory unit' is a 32bits word and the order is the 'natural' least-significant bits first.Bitfields (...) are interpreted as [tt]int[/tt] type which length is given. Adjacent fields in a structure are grouped in memory units depending on the implementation in an implementation-dependant order. When a field following another doesn't fit a partially filled memory unit, it *may* be split between two memory units, or the memory unit *may* be zero-filled
An unnamed field with a 0 width enforces that memory-unit filling so that the next field starts on the next memory unit.
Is that valid? a piece of padding (?) without name?Pype.Clicker wrote:Code: Select all
int :8;
AFAIK, if you make a bitfield of short ints, it should be 16-bit memory units. For chars, 8-bit memory units, for long longs make that 64-bit memory units. Not sure about anything though, but thought it was.Everything i've seen so far tends to prove that on GCC, for IA-32 platforms, the 'memory unit' is a 32bits word and the order is the 'natural' least-significant bits first.
absolutely valid.Candy wrote: Is that valid? a piece of padding (?) without name?
i don't see anything like that in my book. It says bitfield are of int, signed int or unsigned int ...AFAIK, if you make a bitfield of short ints, it should be 16-bit memory units. For chars, 8-bit memory units, for long longs make that 64-bit memory units. Not sure about anything though, but thought it was.
err... sorry if this sounds stupid but there seems to be no semi-colon at the end of the struct. (or is that a typo here)wangpeng wrote: ... but I can give an example from my code...
upon defining an idtentry as
struct idtentry
{
short offset015;
short selector;
char alwayszero;
char type;
short offset1631;
} __attribute__((packed))
No just try this out with "gcc file.c" and execute it (it worked for me in windows)Pete wrote: it wouldn't compile with out the ; so it must be a typo
Pete
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#include<stdio.h>
struct ab{
int a,b,c;
}
main()
{
printf("hello");
}
that's not a problem, that's by design. End all class definitions, type definitions, struct definitions etc. with a semicolon. If you don't know whether one has to be there, place it anyway. Too much doesn't hurt (usually...). Too little does.Neo wrote: the problem here i think is that the compiler thinks the return type of the function is the struct declared before it. (is this right?)
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The packed attribute specifies that a variable or structure field should have the smallest possible alignment--one byte for a variable, and one bit for a field, unless you specify a larger value with the aligned attribute.
Here is a structure in which the field x is packed, so that it immediately follows a:
struct foo
{
char a;
int x[2] __attribute__ ((packed));
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#include <stdio.h>
typedef struct
{
int a;
short b;
char c;
} t1 __attribute__ ((packed));
typedef struct
{
int a __attribute__ ((packed));
short b __attribute__ ((packed));
char c __attribute__ ((packed));
} t2;
t1 var1;
t2 var2;
int main(void)
{
printf("%d\n%d\n", sizeof(var1), sizeof(var2));
return 0;
}
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8
7
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#pragma pack (push, 1)
class DescTable {
public:
uint16 size;
uint32 offset;
};
#pragma pack(pop)
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sizeof(DescTable)well of course they are@proxy: I heard that pragmas were a little unpredicatable when it came to portability between compilers, but again, I dunno firsthand.
, that's the definition of a pragma, a compiler dependant directive...but the __atribute__ stuff will break and simply not compile on non-gcc, the pragmas stand a change of likely being ignored by another compiler..