Clearing allocated memory when using New

[Stonemonkey]

This is causing me a few headaches atm, is there any way to have the memory allocated with New cleared?

[Jim]

No, you'd need to call memset. eg,

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Type *ptr = new Type[THING_COUNT];
memset((void *)ptr, 0, THING_COUNT * sizeof *ptr);


In C you can use calloc, but that's normally implemented as malloc/memset.

Jim

[Stonemonkey]

Ah ok Jim, that's a bit of a pain but thanks.

[Stonemonkey]

Code Select Expand



char *my_new(int bytes)
{
char *new_mem=new char[bytes];
memset (new_mem,0,bytes);
return new_mem;
}

#define _new(type,num_elements) (type*)my_new(sizeof(type)*(num_elements))



would be nicer if I didn't have to specify 1 for a single element though.

EDIT: changed to use New.

[Jim]

Some compilers will let you have

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#define _new(type,num_elements) (type*)my_new(sizeof(type)*(num_elements))
#define _new(type) (type*)my_new(sizeof(type))

defined at the same time and pick the right one depending how many parameters you pass.

I'd be tempted to write the function like this, but them I'm extremely pedantic

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void *my_new(size_t bytes)
{
void *new_mem=(void *)new unsigned char[bytes];
memset(new_mem,0,bytes);
return new_mem;
}

#define _new(type,num_elements) (type*)my_new(sizeof(type) * (num_elements))


The reasons being that void * is the natural type for pointers that we don't know. unsigned char is a better choice than char for the allocation (char can be signed or unsigned, depending on compiler - it makes no difference in this case, but in general, use either 'signed char' or 'unsigned char' unless you're doing stuff with strings).  size_t is the correct type for 'bytes', it's unsigned, but might also be more than 32bits in size.
I'm pretty sure your sample won't compile because memset takes a void * as its first argument and you're passing it char *.  That's an error in C++, but not in C.

Jim

[Stonemonkey]

Ah right, initially I did use void* but decided to change it as I was allocating a number of bytes and It gave no errors or warnings.

Also, I did try the 2 defines but it just replaced the first with the second and gave a warning.

Thanks for that.