Difference between malloc and calloc?

Question

What is the difference between doing:

ptr = (char **) malloc (MAXELEMS * sizeof(char *));

or:

ptr = (char **) calloc (MAXEL         


        

Answer 1

A difference not yet mentioned: size limit

void *malloc(size_t size) can only allocate up to SIZE_MAX.

void *calloc(size_t nmemb, size_t size); can allocate up about SIZE_MAX*SIZE_MAX.

This ability is not often used in many platforms with linear addressing. Such systems limit calloc() with nmemb * size <= SIZE_MAX.

Consider a type of 512 bytes called disk_sector and code wants to use lots of sectors. Here, code can only use up to SIZE_MAX/sizeof disk_sector sectors.

size_t count = SIZE_MAX/sizeof disk_sector;
disk_sector *p = malloc(count * sizeof *p);

Consider the following which allows an even larger allocation.

size_t count = something_in_the_range(SIZE_MAX/sizeof disk_sector + 1, SIZE_MAX)
disk_sector *p = calloc(count, sizeof *p);

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Now if such a system can supply such a large allocation is another matter. Most today will not. Yet it has occurred for many years when SIZE_MAX was 65535. Given Moore's law, suspect this will be occurring about 2030 with certain memory models with SIZE_MAX == 4294967295 and memory pools in the 100 of GBytes.