The STRUCT_ALIGN pragma is similar to DATA_ALIGN, but it can be applied to a structure or union type or typedef. It is inherited by any symbol created from that type. The STRUCT_ALIGN pragma is supported only in C.
The syntax of the pragma is:
| #pragma STRUCT_ALIGN(type, constant expression) |
This pragma guarantees that the alignment of the named type or the base type of the named typedef is at least equal to that of the expression. (The alignment may be greater as required by the compiler.) The alignment must be a power of 2. The type must be a type or a typedef name. If a type, it must be either a structure tag or a union tag. If a typedef, its base type must be either a structure tag or a union tag.
Note that while the top-level object of a type (or a typedef of that type) will be aligned as requested, the type will not be padded to the alignment (as is usual for a struct), nor does the alignment propagate to derived types such as arrays and parent structs. If you want to pad a structure or union so that individual elements are also aligned and/or cause the alignment to apply to derived types, use the "aligned" type attribute described in Section 7.14.4.
Since ANSI/ISO C declares that a typedef is simply an alias for a type (i.e. a struct) this pragma can be applied to the struct, the typedef of the struct, or any typedef derived from them, and affects all aliases of the base type.
This example aligns any st_tag structure variables on a page boundary:
typedef struct st_tag
{
int a;
short b;
} st_typedef;
#pragma STRUCT_ALIGN (st_tag, 128)
#pragma STRUCT_ALIGN (st_typedef, 128)
Any use of STRUCT_ALIGN with a basic type (int, short, float) or a variable results in an error.