10.4.2 Passing Classes Directly on Various Processors
Classes (and unions) that are passed directly by the C++ compiler are passed exactly as the C compiler would pass a struct (or union). However, C++ structs and unions are passed differently on different architectures.
Table 10–1 Passing of Structs and Unions by Architecture|
Architecture |
Description |
|---|---|
|
SPARC V7/V8 |
Structs and unions are passed and returned by allocating storage within the caller and passing a pointer to that storage. (That is, all structs and unions are passed by reference.) |
|
SPARC V9 |
Structs with a size no greater than 16 bytes (32 bytes) are passed (returned) in registers. Unions and all other structs are passed and returned by allocating storage within the caller and passing a pointer to that storage. (That is, small structs are passed in registers; unions and large structs are passed by reference.) As a consequence, small value classes are passed as efficiently as primitive types. |
|
x86 platforms |
Structs and unions are passed by allocating space on the stack and copying the argument onto the stack. Structs and unions are returned by allocating a temporary object in the caller’s frame and passing the address of the temporary object as an implicit first parameter. |
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