Question

Possible Duplicate:
Operator overloading in C

If I have a struct:

typedef struct myStruct {
    ...
} myStruct;

myStruct myStructAdd(myStruct a, myStruct b);

I need something like this:

#define myStruct a + myStruct b myStructAdd(a, b)
// NOTE this code does NOT WORK. This is what the question is asking.

To make this syntax valid:

myStruct a;
myStruct b;
myStruct c = a + b;

Is there any way to use a #define to do this?

EDIT:

I’m not asking for alternatives to the + syntax. What I’m asking is if, and how, the preprocessor can be used to rewrite the plus syntax to standard C syntax on compile.

i.e. something like #define myStruct a + myStruct b myStructAdd(a, b) which turns myStructA + myStructB into myStructAdd(myStructA, myStructB) on compile.

Answer 1

Operator overloading simply isn’t a feature of C or Objective-C. C++ allows you to define arbitrary behaviour for operators and custom types. In Objective-C, if two objects can be added together, then usually there is a method for that:

Foo *result = [foo1 fooByAddingFoo:foo2];

Or, if the class is mutable:

Foo *foo1 = [Foo fooWithBar:bar];

[foo1 addFoo:foo2];

If operator overloading is a must-have feature, use C++ instead, or use Objective-C++ (but keep in mind that C++ classes and Objective-C objects are totally and fundamentally different).

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Edit:

The C proprocessor is conceptually very simple, and it knows very, very little about C’s syntax, and nothing at all about C’s types. If you wanted to overload an operator using the preprocessor, then it would have to learn every type (including custom types) used in your code, and it would have to perform static type checking in order to determine which function to invoke, and this is something that is way out of the scope of the preprocessor.

It’s an interesting idea, but it’s simply not possible.