Classes and objects in C

If, for reasons other than sheer amusement, you need C with classes/objects, you better use C++. This is what C++ is primarily for. However, you can also simulate classes/objects in plain C.

Brief and simple, for that:

1. You ought to use STRUCT of data;
   
   
2. Inside the STRUCT, declare pointers to functions, which will work as the Objects's METHODS, and assign functions' addresses to those pointers;
   
   
3. In order to keep a reference to the Object's context, add an additional STRUCT's property/field as a pointer to the STRUCT itself ("self" in the code below);
   
   
4. This additional Object's field is to be passed to the METHODS in order to access the STRUCT's members.

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#include <stdio.h> struct CLASS { int field1; char *field2; struct CLASS *self; // pointer to itself void (*method1)(struct CLASS *sf); // method 1 int (*method2)(struct CLASS *sf, int del); // method 2 }; void METH1(struct CLASS *sf) { printf("Obj: %d %s\n", sf->field1, sf->field2); } int METH2(struct CLASS *sf, int par) { return sf->field1 * par; } int main(void) { /* --- init the object --- */ struct CLASS obj = { 204, "A string field.", &obj, &METH1, &METH2 }; /* --- prints obj's fields --- */ obj.method1(obj.self); /* --- uses obj's method2 --- */ printf("Field1: %d, Field2: %s, Method2 returns: %d\n", obj.field1, obj.field2, obj.method2(obj.self, 100)); return 0; }

That's it. Of course, no constructors or distructor, no private or protected, no inheritance and suchlike, only basic functionality. This is how the above code would look in C++:

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#include <stdio.h> class CLASS { public: int field1; char *field2; void method1(); // method 1 int method2(int del); // method 2 }; void CLASS::method1() { printf("Obj: %d %s\n", field1, field2); } int CLASS::method2(int par) { return field1 * par; } int main(void) { /* --- init the object --- */ CLASS obj = { 204, (char*)"A string field." }; /* --- prints obj's fields --- */ obj.method1(); /* --- uses obj's method2 --- */ printf("Field1: %d, Field2: %s, Method2 returns: %d\n", obj.field1, obj.field2, obj.method2(100)); return 0; }