13 ms·

Some languages, like Swift, basically do this: they enforce that dynamically allocated objects are definitely initialized before they are used. Also, many C pr

Some languages, like Swift, basically do this: they enforce that dynamically allocated objects are definitely initialized before they are used. Also, many C programmers (in my experience) don't use calloc -- they just use malloc, and then they initialize the memory. The basic danger is that you forget to initialize part of it, and then you have garbage data in your object fields. Zeros are arbitrary, but at least they (usually) cause a seg fault if you try to dereference them as a pointer, for example. I guess there's a secondary danger that even if you do initialize all the fields, you might end up with padding bits that don't get initialized, and those would contain parts of an earlier object. That shouldn't usually matter -- being padding bits, they're not meant to be accessed -- but zeroing them out could act as a security mitigation.

cton 4y ago
Is calloc avoided for a good reason? Or is it something that people should be doing in most cases?
- kragen 4y ago
  it has two arguments
- valleyer 4y ago
  There is often a small amount of extra runtime cost to zero-initialize the buffer. Other than that, no reason other than inertia.
spc476 4y ago
Given the parameters of malloc() and calloc(), I assume it's to express intent---malloc() is used to allocate a single structure (thus, avoiding the whole multiplication issue) and calloc() for allocating an array (and initializing the entire array to a known value). Why realloc() doesn't take an items and size parameters, given that's it's almost always used to resize an array.
sys_64738 4y ago
> Also, many C programmers (in my experience) don't use calloc -- they just use malloc, and then they initialize the memory. The basic danger is that you forget to initialize part of it, I don't know about the latter part of your statement being true or not. The former is due to looping usage so it's better to do bzero as the first operation for use instead of the last for reuse. In other words, don't do the same functionality in two separate areas.

cton 4y ago

Is calloc avoided for a good reason? Or is it something that people should be doing in most cases?

kragen 4y ago
it has two arguments
valleyer 4y ago
There is often a small amount of extra runtime cost to zero-initialize the buffer. Other than that, no reason other than inertia.

spc476 4y ago

Given the parameters of malloc() and calloc(), I assume it's to express intent---malloc() is used to allocate a single structure (thus, avoiding the whole multiplication issue) and calloc() for allocating an array (and initializing the entire array to a known value). Why realloc() doesn't take an items and size parameters, given that's it's almost always used to resize an array.

sys_64738 4y ago

> Also, many C programmers (in my experience) don't use calloc -- they just use malloc, and then they initialize the memory. The basic danger is that you forget to initialize part of it, I don't know about the latter part of your statement being true or not. The former is due to looping usage so it's better to do bzero as the first operation for use instead of the last for reuse. In other words, don't do the same functionality in two separate areas.