Finding Struct Types

**randomalias** · 05-17-2006

In an effort to keep some level of OO in this C version of a C++ program without going overboard with vtable macros and such, I have created 3 kinds of structs which each store information relating to the 3 types of Objects that I used to have in C. Now, to store them in the same array so that they may maintain order and readability, I want to stick them into an array of void pointers. Now the my question is this. Am I able to reference the attributes of the structs pointed to by the void pointers without first casting them back to their original type? If not, is there any other way that I could find out what type of struct the void pointer actually points to? Any help would be appreciated.

**quzah** · 05-17-2006

No. You have to keep track of what type it is. You must typecast any use of a void ponter, unless you're assigning a void pointer to something, in which case, you shouldn't.

Quzah.

**randomalias** · 05-17-2006

Giving it a bit more thought, it occured to me the easiest way to find out what type of struct it is to store a variable/s which tell me what kind of struct it is. Of course, being unable to do this with void pointers, I had the idea that I could typecast the void pointer to each of my know struct types in turn, and then compare the value of the identifier that way. For example, I typecast the void pointer to x StructTypeOne, and then use x.structType as a condition for a selection statement. If structType is not the type I want, I then typecast it to the next type, and so on until the types match. While I am fairly certain this would work, it doesn't appear very efficient or elegant. Is this the only way I can get around the problem or is the a more efficient solution. Thanks for the information :P

**quzah** · 05-17-2006

Code:

struct datatype
{
    size_t type;
    void * data;
};

Use an array of this type of structure.

Code:

size_t type[ X ];

Use an array of type as a catalog of sorts, which stores in its position the type of the corresponding array of your void pointers. There are a few different ways you can do it.

Quzah.

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