Question

I have Googled information on gcc’s __attribute__ ((aligned)) to learn more about how to use the attribute.

According to GNU “You may specify aligned and transparent_union attributes either in a typedef declaration or just past the closing curly brace of a complete enum, struct or union type definition and the packed attribute only past the closing brace of a definition.” In addition the document shows the following example:

struct S { short f[3]; } __attribute__ ((aligned (8)));

But I have found few examples with “typedef struct”. I found the following two:

typedef struct __attribute__ ((aligned)) { char a; int x; } foo;
typedef struct { char a; int x; } __attribute__ ((aligned)) foo;

Which is the preferred method: attribute after struct and before {, or attribute after } and before foo?

Do they both deliver the same result?

I would greatly appreciate any additional detail about the correct usage of __attribute__ ((aligned)) with a typedef:ed struct.

Answer 1

From the GCC doc:

For an enum, struct or union type, you
may specify attributes either between
the enum, struct or union tag and the
name of the type, or just past the
closing curly brace of the definition.
The former syntax is preferred.