Ad:

C Discussion Thread
Unsolved
Views: 3728

May 27th, 2009

calloc and malloc function

Expand Post »

can anyone please tell me the function of calloc() and malloc() and the difference between them ...

what does (char*)malloc(n) mean ??

Similar Threads

free() = delete or delete[]? in C++
Difference between calloc and malloc in C
trying to get text from file in function with malloc in C
Using constructor within a class array in C++
difference between NEW & MALLOC or CALLOC in C++

rocky2008

Reputation Points: 10

Solved Threads: 0

Newbie Poster

Offline

9 posts
since Jun 2008

Permalink

May 27th, 2009

Re: calloc and malloc function

1. calloc, malloc, realloc et al: http://irc.essex.ac.uk/www.iota-six....allocation.asp (or lots of another tutorials on this topic).

2. (type)expression called cast. It forces a conversion of expression value to the type; malloc() returns void* type value (pointer to void) - generic pointer value; char* denotes pointer to char type - so (char*)malloc(n) means dynamically allocate n bytes and get a pointer to this memory as if there are chars into this memory block.

No need to cast void* pointer explicitly in C because void* pointer is converted to any pointer value implicitly. You must convert void* pointer to desired pointer type explicitly in C++, however no needs in malloc call in C++ (it's the other story why).

ArkM

Reputation Points: 1234

Solved Threads: 347

Postaholic

Offline

2,001 posts
since Jul 2008

Permalink

May 27th, 2009

Re: calloc and malloc function

From what I remember, essentially, they both dynamically (while the program is running) allocate memory for your program, and the main difference is that calloc sets all the memory (that it allocates to your program) to zero's while malloc does not. So after calling malloc, the memory that was set aside for your program would still have whatever 0'1 and 1's were in the bits before, but for calloc, all those bits would be set to 0's.

Last edited by BestJewSinceJC; May 27th, 2009 at 4:57 am.

BestJewSinceJC

Reputation Points: 874

Solved Threads: 352

Posting Maven

Offline

2,758 posts
since Sep 2008

Permalink

May 27th, 2009

Re: calloc and malloc function

From the C Standard:

Quote ...

C Syntax (Toggle Plain Text)
void *calloc(size_t nmemb, size_t size);
void *calloc(size_t nmemb, size_t size);
The calloc function allocates space for an array of nmemb objects, each of whose size is size. The space is initialized to all bits zero. Note that this need not be the same as the representation of floating-point zero or a null pointer constant.
...
C Syntax (Toggle Plain Text)
void *malloc(size_t size);
void *malloc(size_t size);
The malloc function allocates space for an object whose size is specified by size and whose value is indeterminate.

None the less look at the link mentioned above.

ArkM

Reputation Points: 1234

Solved Threads: 347

Postaholic

Offline

2,001 posts
since Jul 2008

Permalink

May 27th, 2009

Re: calloc and malloc function

what do you mean in the last line ? can u please explain ?

Click to Expand / Collapse Quote originally posted by BestJewSinceJC ...

From what I remember, essentially, they both dynamically (while the program is running) allocate memory for your program, and the main difference is that calloc sets all the memory (that it allocates to your program) to zero's while malloc does not. So after calling malloc, the memory that was set aside for your program would still have whatever 0'1 and 1's were in the bits before, but for calloc, all those bits would be set to 0's.

rocky2008

Reputation Points: 10

Solved Threads: 0

Newbie Poster

Offline

9 posts
since Jun 2008

Permalink

May 27th, 2009

Re: calloc and malloc function

calloc is essentially this:

c Syntax (Toggle Plain Text)
void *calloc ( size_t n, size_t size )
{
  void *base = malloc ( n * size );
 
  if ( base != NULL )
    memset ( base, 0, n * size );
 
  return base;
}
void *calloc ( size_t n, size_t size )
{
  void *base = malloc ( n * size );

  if ( base != NULL )
    memset ( base, 0, n * size );

  return base;
}

The difference is that the bytes are set to zero with calloc and left as-is with malloc.

Last edited by Narue; May 27th, 2009 at 10:12 am.

Narue

Administrator

Reputation Points: 6442

Solved Threads: 1393

Bad Cop

Offline

11,807 posts
since Sep 2004

Permalink

May 27th, 2009

Re: calloc and malloc function

An obligatory link to http://c-faq.com/malloc/calloc.html

Dave Sinkula

Team Colleague

Reputation Points: 2780

Solved Threads: 312

long time no c

Offline

4,790 posts
since Apr 2004

Permalink

Oct 26th, 2010

-1

Re: calloc and malloc function

give some example
and explain each word.
about malloc and calloc?

surendra verma

Reputation Points: 7

Solved Threads: 0

Newbie Poster

Offline

1 posts
since Oct 2010

This thread is more than three months old

No one has posted to this discussion for at least three months. Please let old threads die and do not reply to them unless you feel you have something new and valuable to contribute that absolutely must be added to make the discussion complete. Otherwise, please start a new thread in this forum instead.

Previous Thread in C Forum Timeline: 2d array passing error

Next Thread in C Forum Timeline: Array Issues in 2D array

DaniWeb Message

Cancel Changes

User Name
Password