I just want to know if C supports over loading? As we use system functions like printf with different no of arguments. Help me out
+13
A:
No, C does not support overloading, but it does support Variadic functions. printf is an example of Variadic functions.
codaddict
2010-02-28 17:10:16
A:
C Does not support overloading. But we can implement that functionality by programming our own library that in turn could provide overloading support.
Karthik Balaguru
2010-02-28 17:11:27
Not sure what you mean. What would a library providing overloading support look like?
sepp2k
2010-02-28 17:12:48
@sepp2k, a bunch of function pointer tables.
Carl Norum
2010-02-28 18:10:08
@Carl: It sounds like you're talking about a vtable. That's for inheritance, I'm not sure how that would help with overloading.
sepp2k
2010-02-28 18:13:50
you can emulate overloading with a function that takes void pointers as arguments - the trick is knowing at runtime what to do with those void pointers, you will probably need type tagging of some sort (you could consider the format string in printf a rudimentary type tagging).
Justin Smith
2010-02-28 22:46:53
+3
A:
No, C doesn't support any form of overloading (unless you count the fact that the built-in operators are overloaded already, to be a form of overloading).
printf works using a feature called varargs. You make a call that looks like it might be overloaded:
printf("%d", 12); // int overload?
printf("%s", "hi"); // char* overload?
Actually it isn't. There is only one printf function, but the compiler uses a special calling convention to call it, where whatever arguments you provide are put in sequence on the stack[*]. printf (or vprintf) examines the format string and uses that to work out how to read those arguments back. This is why printf isn't type-safe:
char *format = "%d";
printf(format, "hi"); // undefined behaviour, no diagnostic required.
[*] the standard doesn't actually say they're passed on the stack, or mention a stack at all, but that's the natural implementation.
Steve Jessop
2010-02-28 17:14:00
I can't speak for all compilers, but the one I work with has the caller adjust the stack for the args it pushed, once the function returns. This seems to be a good idea to me for variadic functions -- safer than having the function pop them from the stack.
tomlogic
2010-02-28 17:42:14
You're right, actually the cdecl calling convention works exactly like that (the caller is responsible for the stack cleanup); I deleted the comment to avoid confusing other readers. The real issue is with scanf, that, if you provide an incorrect format string, may write the data at random locations (taken from the stack) in memory.
Matteo Italia
2010-02-28 17:47:31
+2
A:
No, C doesn't support overloading. If you want to implement overloading similar to C++, you will have to mangle your function names manually, using some sort of consistent convention. For example:
int myModule_myFunction_add();
int myModule_myFunction_add_int(int);
int myModule_myFunction_add_char_int(char, int);
int myModule_myFunction_add_pMyStruct_int(MyStruct*, int);
Magarshak
2010-02-28 17:22:50
+6
A:
It all depends on how you define "support".
Obviously, C language provides overloaded operators within the core language, since most operators in C have overloaded functionality: you can use binary + with int, long and with pointer types.
Yet at the same time C does not allow you to create your own overloaded functions, and C standard library also has to resort to differently-named functions to be used with different types (like abs, fabs, labs and so on).
In other words, C has some degree of overloading hardcoded into the core language, but neither the standard library nor the users are allowed to do their own overloading.
AndreyT
2010-02-28 17:30:10
A:
No c does not support function overloading. But you can get it to compile/work if you are using g++ (a c++ compiler).
chinmaya
2010-02-28 18:08:28
Seconded. If you're using a C++ compiler to compile your code, what you are writing is C++ code, not C code. Especially if you are using features from C++ that are not in C, such as function overloading!
Brooks Moses
2010-02-28 21:40:37
A:
Not directly, and this is not how printf works, but it is possible to create the equivalent of overloaded functions using macros if the types are of different sizes. The type-generic math functions in tgmath.h of the C99 standard may be implemented in that manner.
Pete Kirkham
2010-02-28 18:41:26