How are structure passing and returning implemented?
When structures are passed as arguments to functions, the entire structure is typically pushed on the stack, using as many words as are required. (Programmers often choose to use pointers to structures instead, precisely to avoid this overhead.) Some compilers merely pass a pointer to the structure, though they may have to make a local copy to preserve pass-by-value semantics. Structures are often returned from functions in a location pointed to by an extra, compiler-supplied “hidden” argument to the function. Some older compilers used a special, static location for structure returns, although this made structure-valued functions non-reentrant, which ANSI C disallows.
When structures are passed as arguments to functions, the entire structure is typically pushed on the stack, using as many words as are required. (Programmers often choose to use pointers to structures instead, precisely to avoid this overhead.) Some compilers merely pass a pointer to the structure, though they may have to make a local copy to preserve pass-by-value semantics. Structures are often returned from functions in a location pointed to by an extra, compiler-supplied “hidden” argument to the function. Some older compilers used a special, static location for structure returns, although this made structure-valued functions non-reentrant, which ANSI C disallows. References: ISO Sec. 5.2.3 comp.lang.c FAQ list ยท Question 2.10 Q: How can I pass constant values to functions which accept structure arguments? How can I create nameless, immediate, constant structure values? A: Traditional C had no way of generating anonymous structure values; you had to use a temporary structure vari
