sizeof() Compile time operator

Hi all,

            I am just sharing a small Info on C Trap which I came across yesterday……may be most of u will be familiar with it…but I am jus explaining my experience…

           Scenario:

                          Char *ptr = (char*)malloc(sizeof(char)*30);

                           MyFunc(ptr);

         

                           Void  MyFunc(char *ptr)

{

Int I = sizeof(ptr);  gave me 4 bytes(as ptr is a pointer I mean its storing the address);;;I expected to return entire size allocated USING MALLOC.

I=sizeof(*ptr)   ; gave me 1byte(as the value stored in the address pointed by ptr was char type)

}

 So here ez my list of learnings;

     Actually I used sizeof(ptr); to get the entire memory allocated in main function…but It couldnot be done as sizeof() operator is a compile time operator,and the memory was allocated during runtime.

But after browsing thru net and asking few experienced guys I came to know that it’s the c Limitation in using memory and few latest compilers use some extra memory to keep track of size,datatype,and startpointer..

That is the reason why memset,memcpy fgets will use a 3^rd parmemter to store the size of the destination string……

Happycoding

Avinash