Please explain me this C declaration

[bittware]

A weird C declaration

Could anyone help me to understand what's meaning by the C declaration below?

typedef struct QFreeBlockTag QFreeBlock;
struct QFreeBlockTag {
QFreeBlock *next;
};

I am wondering how the compiler get the clue about what type the pointer points to.

Thanks for your help in advance.

 

[sshahid47]

A weird C declaration

Hi,
what we have here is a simple pointer to its own type and for the compiler, all it has to do is allocate the size required to hold an address(4 bytes), however if you would have

typedef struct QFreeBlockTag QFreeBlock;
struct QFreeBlockTag {
QFreeBlock next;
};

the comiler would throw an error coz the comiler does not know how much to allocate, but for the pointer case it knows that all it has to do is allocate so much to hold the address.

hope that cleared it up.

 

[alitavakol]

Re: A weird C declaration

this is not matter what pointer to use. for each pointers, compiler allocates 4 bytes of memory;
also the size of the overall structure(which contains 4 bytes of pointer variable) determines the required thinks for arithmetic operations on pointer variables.

 

[Zhasha]

Re: A weird C declaration

this structure can basically be used as an empty linked list