Packed union of non-pod structs
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I want to know, is it acceptable to organize data in following manner? Structures is not POD types anymore, due to member initializers, and compiler gives warning about packed attribute being ignored. Is it possible to make them guaranteed packed?
struct StructOne
{
const quint8 h{0x11};
} __attribute__((packed));
struct StructTwo
{
const quint8 h{0x22};
} __attribute__((packed));
struct StructThree
{
quint8 s{0x33}
union
{
StructOne s1;
StructTwo s2;
} __attribute__((packed));
} __attribute__((packed));
struct Top
{
union
{
StructThree s3;
quint8 data[2];
} __attribute__((packed));
} __attribute__((packed));
c++ c++11 member-initialization packed
asked Nov 22 '18 at 22:56
Egor.UttsovEgor.Uttsov
256
|
show 2 more comments
0
I want to know, is it acceptable to organize data in following manner? Structures is not POD types anymore, due to member initializers, and compiler gives warning about packed attribute being ignored. Is it possible to make them guaranteed packed?
struct StructOne
{
const quint8 h{0x11};
} __attribute__((packed));
struct StructTwo
{
const quint8 h{0x22};
} __attribute__((packed));
struct StructThree
{
quint8 s{0x33}
union
{
StructOne s1;
StructTwo s2;
} __attribute__((packed));
} __attribute__((packed));
struct Top
{
union
{
StructThree s3;
quint8 data[2];
} __attribute__((packed));
} __attribute__((packed));
c++ c++11 member-initialization packed
asked Nov 22 '18 at 22:56
Egor.UttsovEgor.Uttsov
256
Currently the size ofTopis 2 bytes assumingqunit8to be the size of achar. You expect it to go lower than that?
– P.W
Nov 23 '18 at 6:28
@P.W I expect that it wouldn't be greater, that 2 bytes. Is this structure still be packed?
– Egor.Uttsov
Nov 23 '18 at 12:16
It can't go lower than 2 bytes. The size of the union will be at least 2 bytes. So I believe its packed already.
– P.W
Nov 23 '18 at 12:21
@P.WThe main question - is it possible to receive a padding on some platforms?
– Egor.Uttsov
Nov 23 '18 at 12:56
I think it depends on whether the compiler can guarantee "packedness" with this attribute, then platform will not matter.
– P.W
Nov 23 '18 at 12:59
|
show 2 more comments
0
0
0
I want to know, is it acceptable to organize data in following manner? Structures is not POD types anymore, due to member initializers, and compiler gives warning about packed attribute being ignored. Is it possible to make them guaranteed packed?
struct StructOne
{
const quint8 h{0x11};
} __attribute__((packed));
struct StructTwo
{
const quint8 h{0x22};
} __attribute__((packed));
struct StructThree
{
quint8 s{0x33}
union
{
StructOne s1;
StructTwo s2;
} __attribute__((packed));
} __attribute__((packed));
struct Top
{
union
{
StructThree s3;
quint8 data[2];
} __attribute__((packed));
} __attribute__((packed));
c++ c++11 member-initialization packed
asked Nov 22 '18 at 22:56
Egor.UttsovEgor.Uttsov
256
I want to know, is it acceptable to organize data in following manner? Structures is not POD types anymore, due to member initializers, and compiler gives warning about packed attribute being ignored. Is it possible to make them guaranteed packed?
struct StructOne
{
const quint8 h{0x11};
} __attribute__((packed));
struct StructTwo
{
const quint8 h{0x22};
} __attribute__((packed));
struct StructThree
{
quint8 s{0x33}
union
{
StructOne s1;
StructTwo s2;
} __attribute__((packed));
} __attribute__((packed));
struct Top
{
union
{
StructThree s3;
quint8 data[2];
} __attribute__((packed));
} __attribute__((packed));
c++ c++11 member-initialization packed
c++ c++11 member-initialization packed
asked Nov 22 '18 at 22:56
Egor.UttsovEgor.Uttsov
256
asked Nov 22 '18 at 22:56
Egor.UttsovEgor.Uttsov
256
asked Nov 22 '18 at 22:56
Egor.UttsovEgor.Uttsov
256
asked Nov 22 '18 at 22:56
Egor.UttsovEgor.Uttsov
256
asked Nov 22 '18 at 22:56
Egor.UttsovEgor.Uttsov
256
256
Currently the size ofTopis 2 bytes assumingqunit8to be the size of achar. You expect it to go lower than that?
– P.W
Nov 23 '18 at 6:28
@P.W I expect that it wouldn't be greater, that 2 bytes. Is this structure still be packed?
– Egor.Uttsov
Nov 23 '18 at 12:16
It can't go lower than 2 bytes. The size of the union will be at least 2 bytes. So I believe its packed already.
– P.W
Nov 23 '18 at 12:21
@P.WThe main question - is it possible to receive a padding on some platforms?
– Egor.Uttsov
Nov 23 '18 at 12:56
I think it depends on whether the compiler can guarantee "packedness" with this attribute, then platform will not matter.
– P.W
Nov 23 '18 at 12:59
|
show 2 more comments
Currently the size ofTopis 2 bytes assumingqunit8to be the size of achar. You expect it to go lower than that?
– P.W
Nov 23 '18 at 6:28
@P.W I expect that it wouldn't be greater, that 2 bytes. Is this structure still be packed?
– Egor.Uttsov
Nov 23 '18 at 12:16
It can't go lower than 2 bytes. The size of the union will be at least 2 bytes. So I believe its packed already.
– P.W
Nov 23 '18 at 12:21
@P.WThe main question - is it possible to receive a padding on some platforms?
– Egor.Uttsov
Nov 23 '18 at 12:56
I think it depends on whether the compiler can guarantee "packedness" with this attribute, then platform will not matter.
– P.W
Nov 23 '18 at 12:59
Currently the size of
Top is 2 bytes assuming qunit8 to be the size of a char. You expect it to go lower than that?– P.W
Nov 23 '18 at 6:28
Currently the size of
Top is 2 bytes assuming qunit8 to be the size of a char. You expect it to go lower than that?– P.W
Nov 23 '18 at 6:28
@P.W I expect that it wouldn't be greater, that 2 bytes. Is this structure still be packed?
– Egor.Uttsov
Nov 23 '18 at 12:16
@P.W I expect that it wouldn't be greater, that 2 bytes. Is this structure still be packed?
– Egor.Uttsov
Nov 23 '18 at 12:16
It can't go lower than 2 bytes. The size of the union will be at least 2 bytes. So I believe its packed already.
– P.W
Nov 23 '18 at 12:21
It can't go lower than 2 bytes. The size of the union will be at least 2 bytes. So I believe its packed already.
– P.W
Nov 23 '18 at 12:21
@P.WThe main question - is it possible to receive a padding on some platforms?
– Egor.Uttsov
Nov 23 '18 at 12:56
@P.WThe main question - is it possible to receive a padding on some platforms?
– Egor.Uttsov
Nov 23 '18 at 12:56
I think it depends on whether the compiler can guarantee "packedness" with this attribute, then platform will not matter.
– P.W
Nov 23 '18 at 12:59
I think it depends on whether the compiler can guarantee "packedness" with this attribute, then platform will not matter.
– P.W
Nov 23 '18 at 12:59
|
show 2 more comments
0
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Currently the size of
Topis 2 bytes assumingqunit8to be the size of achar. You expect it to go lower than that?– P.W
Nov 23 '18 at 6:28
@P.W I expect that it wouldn't be greater, that 2 bytes. Is this structure still be packed?
– Egor.Uttsov
Nov 23 '18 at 12:16
It can't go lower than 2 bytes. The size of the union will be at least 2 bytes. So I believe its packed already.
– P.W
Nov 23 '18 at 12:21
@P.WThe main question - is it possible to receive a padding on some platforms?
– Egor.Uttsov
Nov 23 '18 at 12:56
I think it depends on whether the compiler can guarantee "packedness" with this attribute, then platform will not matter.
– P.W
Nov 23 '18 at 12:59