Hi,

I know the basic difference between malloc and calloc i.e the memory allocated with malloc is not initialized while with calloc its initialized to zero.

why there are 2 different functions as malloc and calloc if we can get the same functionality as calloc with malloc and memset?

Also I have observed that, in programes most of the time we allocate memory dynamically using malloc.

I would like to know where exactely we will use calloc instead of malloc? any particular application?

clearly not a member intro. moved to programming.

I use calloc when I would otherwise have to use malloc and memset... You're question strikes me as being like asking "why is there a command to print strings when we can just loop through and print characters"...

Sometimes you'll be writing information before you read it, in which case using calloc() causes unnecessary memory writing. For example, if I want to copy a string into a chunk of new address space, all I need to do is malloc() and then write the string in. If I use calloc() instead, it will zero out the new space, which is not needed because I'm just going to overwrite it anyway. Remember that a lot of these functions (especially in C) come from a time where execution speed was very important. Re-writing hundreds of kilobytes of memory unnecessarily was a huge waste of time.

If you think that's weird, you should try Perl: "There's more than one way to do it!"

Indeed.

Execution time is IMHO still important, and malloc is still far superior to calloc as it takes virtually no time to execute while calloc can be resource demanding.
You can malloc whatever size you want in far less than a microsecond, while "callocating" memory will take something like 300 milliseconds per gigabyte (YMMV), and much more if you are short of RAM and start swapping.

Thanks for the reply.
still 1 doubt in malloc and calloc...

I read some where that memory allocated by malloc is not contiguous while with calloc its contiguous. or vice a versa.
I am not sure.

but is it true?

a chunk of allocated memory is always logically contiguous. There's lots of fun stuff that the OS does behind your back with Virtual Memory that means that an allocated chunk of memory may not be contiguous physically, or even in memory at all!

With malloc not only the allocated memory won't be in RAM at all at the time of allocation, but with Linux the returned pointer may even point to memory that neither exist in virtual memory. This is known as over-committing memory.

calloc is probably implemented using malloc.
the memory from each call will of course, from your point of view, be contiguous, it would be useless otherwise. Each byte byte will be accesed as next to it's neighbour regardless of where it lies in reality, on disk or RAM or cache.
That is the operating system's problem, not yours.

My point is that the next byte may lie neither in RAM, disk or cache with Linux and other O/Ses allowing over-commiting.

If you are sure you'll use all of the memory you allocate, that make sense to call the slower calloc, as you'll know in the first place the virtual memory you are asking for actually exists, and the time lost during the calloc will be compensated by the time saved when filling the memory with your data.

ok Jilliagre was not bumping you, was just trying to simplify for the OP

No problem. Thanks

ISO C 99 says this:

This is where Linux (and some commercial Unix-es too) are borderline with the standard.