Question

I want to write a linked list that can have the data field store any build-in or user-define types. In C++ I would just use a template, but how do I accomplish this in C?

Do I have to re-write the linked list struct and a bunch of operations of it for each data type I want it to store? Unions wouldn’t work because what type can it store is predefined.

Answer 1

There are different approaches to this problem:

• using datatype void*: these means, you have pointers to memory locations whose type is not further specified. If you retrieve such a pointer, you can explicitly state what is inside it: *(int*)(mystruct->voidptr) tells the compiler: look at the memory location mystruct->voidptr and interpret the contents as int.

• another thing can be tricky preprocessor directives. However, this is usually a very non-trivial issue:

• I also found http://sglib.sourceforge.net/

Edit: For the preprocessor trick:

 #include <stdio.h>

 #define mytype(t) struct { t val; }

 int main(int argc, char *argv[]) {
   mytype(int) myint;
   myint.val=6;
   printf ("%d\n", myint.val);
   return 0;
 }

This would be a simple wrapper for types, but I think it can become quite complicated.