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cdata-structuresfunction-pointers
Saucy Goat
Saucy Goat

Reputation: 1675

Use of function pointers in C on data structure development

I'm having an Algorithms course next semester and so I dived into C with the purpose of making a few data structures ahead of time to be prepared.

As I learned about function pointers, I found I could store them in structs and create an object-oriented-like use for my data structure. Here's an example:

#include <stdio.h>


void insert(char * object)
{
    printf("Adding %s to the data structure\n", object);
}


typedef struct data_structure {
    char * obj;
    void (*insert)(char * object);
} data_structure;


int main()
{
    data_structure d;
    d.insert = insert;

    d.insert("bacon");

    return 0;
}

But is this kind of procedure actually useful in the scope of data structure and algorithm studying in C? Or is it just taking up memory on the data structure?

I've found other posts talking about function pointers, but none that explores this kind of approach. I think this could be useful to a bunch of curious students out there :)

Upvotes: 2

Views: 472

Answers (2)

Saucy Goat
Saucy Goat

Reputation: 1675

After reading all the answers, here's the insight this post gathered regarding the use of function pointers as C structure attributes.

Advantages:

  • Good ol' practise on a somewhat advanced subject if you're a student
  • Provides encapsulation and object oriented code in C
  • Gives you better understanding of the object orientated programming paradigm if you're not already well familiarized with it
  • Can be used to implement VTables

Disadvantages:

  • On a functional level, you still have to pass the data structure to the function, as it doesn't have access to said data structure
  • Slight performance overhead

In conclusion, the use of function pointers as in the original question would really only have practical uses if one wishes to explore OOP whilst getting into more advanced aspects of C, or to construct VTables.

Thank you to all the people who replied.

Upvotes: 0

Gem Taylor
Gem Taylor

Reputation: 5613

In the past I have certainly seen objects constructed this way as sets of function pointers effectively representing a vtable. Usually, for a vtable you add one extra level of indirection such that all data objects with similar traits point to the same function pointer object. This reduces the cost per data object if there is more than 1 function, but at a slight execution cost.

It can also be used as a lightweight way to organise and structure function+voiddata callback objects, by insisting that the first member of the data is the callback function. Of course, you can't define inherited classes using c, but you can have nested structures which can be bullied to the same purpose.

Upvotes: 1

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