Does gcc has compile option for bytes alignment?

[Allen]

I know how to specify bytes alignment for a struct, i.e. using
__attribute__((aligned(4))).
But it is unconvenient because it must modify all struct, union and
class declaration.
Is there a compile option for gcc to define global bytes alignment?

For example, something looks like
#gcc -faligned4 -o test test.cpp

Thank you.
Allen

 

[Lionel B]

I know how to specify bytes alignment for a struct, i.e. using
__attribute__((aligned(4))).
But it is unconvenient because it must modify all struct, union and
class declaration.
Is there a compile option for gcc to define global bytes alignment?

For example, something looks like
#gcc -faligned4 -o test test.cpp

This ng does not deal with compiler-specific issues; you're more likely to
get help in a gcc forum such as gnu.gcc.help or gnu.g++.help

Thanks,

 

[Maxim Yegorushkin]

I know how to specify bytes alignment for a struct, i.e. using
__attribute__((aligned(4))).
But it is unconvenient because it must modify all struct, union and
class declaration.

Why would you want to do that?

Is there a compile option for gcc to define global bytes alignment?

There probably is:
http://gcc.gnu.org/onlinedocs/gcc-4...ng-Pragmas.html#Structure_002dPacking-Pragmas

 

[Allen]

Why would you want to do that?


There probably is:http://gcc.gnu.org/onlinedocs/gcc-4.3.2/gcc/Structure_002dPacking-Pra...

I have tested option -fpack-struct=8 and #pragma pack(8), both fails
to take effects.
Only __attribute__((aligned(8)) works.

Allen

 

[Maxim Yegorushkin]

I have tested option -fpack-struct=8 and #pragma pack(8), both fails
to take effects.

How did you check that?

 

[Allen]

How did you check that?

union Test
{
char c;
int i;
float f;
};

I print sizeof(Test), when using -fpack-struct=8 and #pragma pack(8)
it outputs 4, while using __attribute__((aligned(8))) it outputs 8,
i.e. as same as set value.

Allen

 

[Maxim Yegorushkin]

union Test
{
char c;
int i;
float f;

};

I print sizeof(Test), when using -fpack-struct=8 and #pragma pack(8)
it outputs 4, while using __attribute__((aligned(8))) it outputs 8,
i.e. as same as set value.

The description says "... a set of #pragma directives which change the
maximum alignment of members of structures..." It is probably not what
you want.