Memory Management

[DeliriumCordia]

Hi guys,
I'm a beginner in C and I need to handle memory. I have lot of arrays, most of all of pretty big size, and I'd like to know if I'm using fine the memory management.

complex *originalSignal = malloc(OVERLENGTH*sizeof(complex)); 
    complex *noisevector = malloc(OVERLENGTH * sizeof (complex)); 
    complex *receivedSignal = malloc(OVERLENGTH * sizeof (complex));
   complex *copiaOriginale = malloc(OVERLENGTH * sizeof (complex));
complex *crossCorrVect;

I generate 4 arrays of size of OVERLENGTH complex items.
The last one is a simple pointer that will become an array. A function gets this pointer as parameter and builds an array; the size of this array is determined by the function, so I don't know if I should malloc here in the main, or just declarate the variable even in the function without using malloc.

By the way, my main function goes on: when I need to free space with these arrays I just need to do:

free(copiaOriginale);
free(originalSignal);
...

Is it wrong to do the same with the array crossCorrVect, which I didn't allocate with malloc?

free(crossCorrVect);

Is there a way to check if i really deleted the arrays?

I tried to make a check like:

if(originalSignal[randomindex]==NULL)
printf("ok");

but I get == as invalid operator.

[laserlight]

The last one is a simple pointer that will become an array. A function gets this pointer as parameter and builds an array; the size of this array is determined by the function, so I don't know if I should malloc here in the main, or just declarate the variable even in the function without using malloc.

It sounds like the function will be doing the malloc, hence there is no point using malloc at this point. Instead, initialise the pointer to be a null pointer.

Is it wrong to do the same with the array crossCorrVect, which I didn't allocate with malloc?

It depends. What does this mysterious function that you talked about do? If it allocates memory using malloc (or calloc or realloc) then yes, otherwise, no.

Is there a way to check if i really deleted the arrays?

Yes, if you set the pointers to be null pointers immediately after calling free on them.

[DeliriumCordia]

So each time i declare a pointer it should point to NULL?

And after i free arrays i should declare again pointer=NULL?

[laserlight]

So each time i declare a pointer it should point to NULL?

Yes, if you are not going to immediately make it point to something. (It does not really "point to NULL". Rather, its value is set to NULL, hence it is a null pointer.)

And after i free arrays i should declare again pointer=NULL?

Yes, if the pointer is not going to go out of scope soon after, or otherwise will most certainly not be used.

[DeliriumCordia]

Ok, thank you very much.

Another question. For the crossCorrVect I was talking about, I create a pointer to the array that will be created in a specific function. It will point to the first element of the vector generated by the function.

Is it wrong to malloc the array in the function, and to free it in the main when it becomes unnecessary?

[laserlight]

No, that is not wrong.

[DeliriumCordia]

Thank you very much, very kind

[grumpy]

Yes, if you are not going to immediately make it point to something. (It does not really "point to NULL". Rather, its value is set to NULL, hence it is a null pointer.)


Yes, if the pointer is not going to go out of scope soon after, or otherwise will most certainly not be used.

An alternative to initialising a pointer to NULL (if it is not going to be used immediately) is to ensure the pointer is not created until it is needed.

Similarly, the obvious alternative to setting a pointer to NULL if it is not going out of scope is to ensure it does go out of scope.

It is quite easy to create a new scope within a function using curly braces, or to create a new function (which also has its own scope). It is then easy to ensure a pointer is created and memory allocated to immediately in the new scope, and similarly it is easy deallocation immediately before the pointer passes out of scope.

Things are a little trickier if you need a pointer (or memory malloc'd to it) to exist outside the scope it is created. Then the initialising or setting to NULL techniques are certainly options, although I disagree with using them routinely.