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i cant understand this line
i know that if we have enough memory malloc returns void pointerCode:ptr = malloc(number*sizeof(int));
and if not then null pointer
but here by protocol i need to have an address something like
ptr=&x
there is no address on the right side
??
malloc returns an address in itself. You do not need &.
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Mats
The & symbol means the address of the variable. So in your case it will mean that store to p the address of x.
What malloc does is finds you a piece of memory. Then returns a pointer to the beginning of the memory. THAT pointer that is returns, the void pointer, has the memory address stored to it.
Remember that pointers have values that represent memory addresses.
ok so in void pointer case he will return an address to the starting of the empty section in the memory.
what will he return in the null pointer case(when there is not enough free space)
??
in this line there must be an address on the right side
Code:ptr = malloc(number*sizeof(int));
there is no address to return
NULL is also a pointer.
Obviously, malloc returns a null pointer in "the null pointer case".Quote:
Originally Posted by transgalactic2
what is the address of null pointer?
There is no such a thing. The value of a NULL pointer is (almost always) the address 0.
NULL means nothing. Consequently NULL pointer means pointing to nothing. That is, the pointer returned by the malloc is pointing no where (This is true if the malloc failed to allocate space in the memory!!!). Hence its always a good practice to check if the malloc returned NULL.
Hence when you declare a pointer, in most code you initialise it NULL. What you are trying to say there is the pointer is pointer no where explicitly to the compiler to avoid confusion.
ssharish
Zero (or something equivalent to zero - in general we do not need to worry about the value of NULL, but comparing a pointer with zero should give the same result as comparing with NULL).Quote:
Originally Posted by transgalactic2
[Although if I may be pedantic, the address of a NULL pointer is undefined, the VALUE of the pointer is zero, just like the address of the returned value when malloc succeeds is undefined, but the address value that is returned represents memory that you can use in your code - you STORE the address value in a pointer].
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Mats
Strictly speaking, NULL is a null pointer constant.Quote:
Originally Posted by tabstop
The address of the pointer would be &ptr. Very defined. Also, a pointer that is equal to NULL (indicating invalid) is NOT necessarily guaranteed to be a zero. Now that's pedantic. See how annoying it is to be pedantic? Not directed at matsp in particular. Just the cranky long timers here.
More pedantry: But there is no address of the RETURN value from the function, there is indeed an address of the local variable where the result is eventually stored. NULL is indeed not guaranteed to be zero, but comparing to zero and comparing to NULL should have the same effect in a compiler that follows the C standard. If the compiler doesn't follow the standard, then all bets are off.Quote:
Originally Posted by nonoob
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Mats
Pedantic? That's debatable. A pointer is never directly compared to a null pointer constant since a null pointer constant is converted to a null pointer for the comparison. A null pointer is not invalid, just not dereferenceable. NULL itself is guaranteed to have the value of zero, though whether that zero is 0 or (void*)0 is implementation defined.Quote:
Originally Posted by nonoob