C 铸造结构的返回值

Question

On an old C compiler that only passes structures by pointers I fortunately have a structure that is 4 bytes long. Which is the size of a long (not int) on this system.

The code I'm porting (awk V7 or 32V) has many functions that return this structure by value.

I'm trying to find a way to cast the structure a long and visa versa and while I have managed this for variables the cast fails with the return value of a function. I would be forced to use a temp long and then cast that. This means more than a simple define to solve my issue and means avoidable recoding.

Is there a way I can do this with just defines?

I have some sample code here that I'm playing around with. Sample code from different system has long of 64 bits so using int32 as long.

#include <stdio.h>

typedef struct _obj { char a; char b; short c; } Obj;

#define OBJ2INT *(int32*)&
#define INT2OBJ *(Obj*)&

/* Obj */ int32 newObj(a, b, c) /* was returing Obj */
char a; char b; int c;
{
    Obj newobj;
    newobj.a = a;
    newobj.b = b;
    newobj.c = c;
    return OBJ2INT newobj;
}

int main(argc, argv)
int argc; char *argv[];
{
    Obj a, b;
    int32 t;

    t = newObj('a', '1', 1));
    a = INT2OBJ t; /* this works but require recoding with a temp variable */
    b = INT2OBJ newObj('b', '2', 2); /* this is not allowed. even though the value is on the stack there is no address for return value */

    printf("a = %c %c %d\n", a.a, a.b, a.c);
    printf("b = %c %c %d\n", b.a, b.b, b.c);
}

Answer 1

I was missing the whole point. K & R C cannot assign or pass structures/unions.

So converting the int32 to a structure and assigning to another structure is never going to work. Can't assign structures. So the structure must always be converted to an int32. because int32 can be assigned and passed: The solution was to change this :

b = INT2OBJ newObj('b', '2', 2); /* this is not allowed. even though the value is on the stack there is no address for return value */

to this:

   OBJ2INT b = newObj('b', '2', 2);

INT2OBJ is never required. What was required was moving the INT2OBJ from the right to a OBJ2INT on the left of the assignment!