return void* pointer from function into other function parameter

Question

I'm, trying to build a generic list that handles Element(s) each object (pointer to struct) in the program should use this list,

that's the definition for void*, from now on it's Element. and the add function signature:

typedef void* Element;
void AddElementToList(List thisList , Element toAdd);

and the create user function and the user definition:

typedef struct FacebookUser_t* User;
User CreateUser(char* const lineToSplit);

that's how i call the function:

AddElementToList(thisServer->UsersList , (Element)CreateUser(line));

while debugging the create user function doing good and values assigned to it, just after it return it seems that the object become empty and then at the add element it crushes. that's the return :

return toAdd;

'toAdd' it's User type. What am I doing wrong?

Can't tell what's wrong without seeing the relevant parts of CreateUser and AddElementToList. Sounds like you're mis-using stack-based objects, but could be anything. — Mat
– Mat, Commented Dec 17, 2011 at 10:46
Hiding pointers behind typedefs is a bad idea; the semantics of pointers are fundamentally different, and hiding that can lead to code that is confusing to read. — Oliver Charlesworth
– Oliver Charlesworth, Commented Dec 17, 2011 at 10:57
Btw, const in the above makes lineToSplit, the pointer, not what it points to, constant. You probably want it the other way around: char const* lineToSplit or const char* lineToSplit (they're equivalent). — Alexey Frunze
– Alexey Frunze, Commented Dec 17, 2011 at 10:58

Johan Bezem · Accepted Answer · 2011-12-17 17:06:46Z

1

Difficult to say without more information, but you need to watch out for object scope: - your CreateUser function has to allocate memory for a FacebookUser_t object on the heap, using malloc or similar, returning a pointer to that (type User; that's why @OliCharlesworth is warning about hiding pointers behind a typedef: User is not a user-object, and does not allocate memory).

Your last line suggests another possible problem. You indicated toAdd to be a parameter to the function AddElementToList, then you talk about returning 'toAdd', but the function is of type 'void'. Something is confusing here IMHO, and you might want to review those sections.

answered Dec 17, 2011 at 17:06

Johan Bezem

2,5931 gold badge21 silver badges47 bronze badges

Sign up to request clarification or add additional context in comments.

Collectives™ on Stack Overflow

return void* pointer from function into other function parameter

1 Answer 1

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

Comments

Your Answer

Sign up or log in

Post as a guest

Related