Very Computer

by **Frank Popp** » Thu, 23 Dec 1999 04:00:00

Hi all,

I'm porting an old DOS app now to linux, at least some small exe's, for
the use as cgi-scripts to access an some database files. The dos-exes
where compiled with an 1 byte alignment, and now i need to do this in my
gcc-linux program also. the db-structure used is:

typedef struct {
/* 0 */ UCHAR name[53] __attribute__ ((aligned (1)));
/* 53 */ ULONG number __attribute__ ((aligned (1)));
/* 57 */ UCHAR name2[53] __attribute__ ((aligned (1)));
} mystruct;

But the align-attribute doesn't give the desired results, it will be
aligned on 2 or 4 byte boundaries, so that from name2 always the first
three chars are missing.

Can anyone hlep to acomplish that?

Thanks

by **Anthony Gree** » Thu, 23 Dec 1999 04:00:00

> I'm porting an old DOS app now to linux, at least some small exe's, for
> the use as cgi-scripts to access an some database files. The dos-exes
> where compiled with an 1 byte alignment, and now i need to do this in my
> gcc-linux program also. the db-structure used is:

> typedef struct {
> /* 0 */ UCHAR name[53] __attribute__ ((aligned (1)));
> /* 53 */ ULONG number __attribute__ ((aligned (1)));
> /* 57 */ UCHAR name2[53] __attribute__ ((aligned (1)));
> } mystruct;

> But the align-attribute doesn't give the desired results, it will be
> aligned on 2 or 4 byte boundaries, so that from name2 always the first
> three chars are missing.

Use __attribute__((packed)) instead. From the GCC manual:

AG

--
Anthony Green Cygnus Solutions
Sunnyvale, California

by **Norm Dresne** » Fri, 24 Dec 1999 04:00:00

#pragma pack(1)
causes no added space for alignment

Norm

> > > I'm porting an old DOS app now to linux, at least some small exe's,
for
> > > the use as cgi-scripts to access an some database files. The dos-exes
> > > where compiled with an 1 byte alignment, and now i need to do this in
> my
> > > gcc-linux program also. the db-structure used is:

> > > typedef struct {
> > > /* 0 */ UCHAR name[53] __attribute__ ((aligned (1)));
> > > /* 53 */ ULONG number __attribute__ ((aligned (1)));
> > > /* 57 */ UCHAR name2[53] __attribute__ ((aligned (1)));
> > > } mystruct;

> > > But the align-attribute doesn't give the desired results, it will be
> > > aligned on 2 or 4 byte boundaries, so that from name2 always the
first
> > > three chars are missing.

> #pragma pack(n)
> changes the alignment to n=2,4 (and maybe 8).
> #pragma pack()
> resets it to the default

> Norm

by **Norm Dresne** » Fri, 24 Dec 1999 04:00:00

> > I'm porting an old DOS app now to linux, at least some small exe's, for
> > the use as cgi-scripts to access an some database files. The dos-exes
> > where compiled with an 1 byte alignment, and now i need to do this in
my
> > gcc-linux program also. the db-structure used is:

> > typedef struct {
> > /* 0 */ UCHAR name[53] __attribute__ ((aligned (1)));
> > /* 53 */ ULONG number __attribute__ ((aligned (1)));
> > /* 57 */ UCHAR name2[53] __attribute__ ((aligned (1)));
> > } mystruct;

> > But the align-attribute doesn't give the desired results, it will be
> > aligned on 2 or 4 byte boundaries, so that from name2 always the first
> > three chars are missing.

#pragma pack(n)
changes the alignment to n=2,4 (and maybe 8).
#pragma pack()
resets it to the default

Norm

by **wim delvau** » Wed, 29 Dec 1999 04:00:00

I Wonder if the ULONG will be usable in the application to perform
calculations (if at all necessary)

> #pragma pack(1)
> causes no added space for alignment

> Norm

> > > > I'm porting an old DOS app now to linux, at least some small exe's,
> for
> > > > the use as cgi-scripts to access an some database files. The dos-exes
> > > > where compiled with an 1 byte alignment, and now i need to do this in
> > my
> > > > gcc-linux program also. the db-structure used is:

> > > > typedef struct {
> > > > /* 0 */ UCHAR name[53] __attribute__ ((aligned (1)));
> > > > /* 53 */ ULONG number __attribute__ ((aligned (1)));
> > > > /* 57 */ UCHAR name2[53] __attribute__ ((aligned (1)));
> > > > } mystruct;

> > > > But the align-attribute doesn't give the desired results, it will be
> > > > aligned on 2 or 4 byte boundaries, so that from name2 always the
> first
> > > > three chars are missing.

> > #pragma pack(n)
> > changes the alignment to n=2,4 (and maybe 8).
> > #pragma pack()
> > resets it to the default

> > Norm

Very Computer

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gcc - alignment

gcc - alignment

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