Implement malloc()

[rahuls]

Hi,
Can anyone suggest any idea or some C code to implement malloc function. The point is how will you find the amount of memory present in the heap and allocate it.
Please try to explain the code as I am sure it would be complicated.
Thanks.

[tigs]

Dynamic 2D array of longs:

// Malloc returns a pointer to the beginning of the array you just initialised
// (long*) is a typecast telling the compiler that malloc is returning a pointer to an array of longs
long *pointer = (long*)malloc(length * width * sizeof(long));

if (pointer == NULL) {
    // Do something error-like (malloc returns null if failed to allocate memory)
}

//From now on we can use it like a 1-dimensional array, use this formula to write a 2D position:
pointer[(y * width) + x] = value;

// When done, you MUST do this:
free(pointer);

[rahuls]

Hi tigs,
Thanks for responding. However I think you didnt get my question. I want to know how is the malloc function actually written in the system library. I mean what would be the contents/definition of the function. How would the function figure out how much heap memory is remaining and how would it allocate it.
Thanks.

[Magos]

Originally posted by rahuls
Hi tigs,
Thanks for responding. However I think you didnt get my question. I want to know how is the malloc function actually written in the system library. I mean what would be the contents/definition of the function. How would the function figure out how much heap memory is remaining and how would it allocate it.
Thanks.

We are not allowed to know that...
It's up to each compiler.

[Prelude]

>The point is how will you find the amount of memory present in the heap and allocate it.
You would use a system level function or other implementation/system dependent method to acquire core memory from the free store. malloc is one of the functions that will probably be wildly different for every system.

-Prelude

[Codeplug]

Here's how GNU did it.

gg