Pointer to functions

Hi,

How do I use default values in pointers to functions, say I want to do this,

Code:

---

typedef struct {
void (*append)(int,int)
} LOGVTBL;

LOGVTBL log = {LogAppend};


void LogAppend(int x, int y=10) {
//some code
}

then I want to be able to do:

logvt.append(10) ;
logvt.append(10,15);

---

Please help!

Default arguments are C++?

Is there any way of taking several arguments but only using the ones that are passed to the function?

There's a few alternative solutions:

1) Create as many functions as you want to have a different number of arguments for. For example, you could make a func2() which takes 2 arguments, func4() which takes 4 arguments, etc.

2) Use a variable arguments parameter like printf() does. Something like: return_type func(int numargs, ...); Then you'd just pass the number of arguments first like func(3, 10, 20, 30);

3) Create one function that accepts the maximum number of arguments you're going to pass it. Then have a "use default" value for them. Say your function expects up to 3 positive integers. You could have a check to see if each argument is less than 0 and if it is you could set it to some default value. Like: if(arg2 < 0) arg2 = 8;

You just have to be creative. Use a method that works best for you. Either that or switch to C++ where you have polymorphism.

C99 allows function overloading

Quote:

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C99 allows function overloading

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Where does the C99 standard say that? I don't remember reading it anywhere, and I can't find it right now...but that could be the Guinness' fault. :p

Quote:

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Originally Posted by sand_man

C99 allows function overloading

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(I think :))

[edit] ok so maybe I was wrong

I would use variable arguments.

This seems very static, I don't want to change the exsiting code, I just want to add functionality to an already exsiting function.
Isn't there anything more similar to default values in c++?

I don't want to pass any values apart from the ones that are to be treated.
Like i said.....

logvt->append(1)
logvt->append(1,2)

No values concerning the number of args or anything like that....

Can anyone tell me if this is possible in c?

No, it's not possible in C. The closest approximation to that is variable arguments, but you need a parameter to specify the number of arguments passed.

If you were feeling really perverted, you could write a custom preprocessor for your C program which mangled your append calls into two separate functions, effectively emulating overloading.

Try this,

Code:

---

#include <stdio.h>

typedef int (*func_ptr)();

int add (int a, int b)
{
  return (a+b);
}

int sqr (int a)
{
  return (a*a);
}

int main()
{
  func_ptr fp;
 
  fp = add;
 
  printf("Sum of 2 and 3 is %d\n",fp(2,3));

  fp = sqr;
 
  printf("square of 2 is %d\n",fp(2));

  return 0; 
}

---

Program Output

Quote:

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[root@olinux1 tools]# ./ptrfunc
Sum of 2 and 3 is 5
square of 2 is 4
[root@olinux1 tools]#

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nkhambal, that is an abomination :P

Not really shure what you wanted to achieve by that nkhambal!!!

oops sorry!!! I think, I lost the objective in OP. My apologies. I though the OP wanted to know how to use a single function pointer to call multiple functions which accepts different number of arguments.
Example is still valid , although not related to the OP :p