calloc and malloc function

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calloc and malloc function

 
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May 27th, 2009
can anyone please tell me the function of calloc() and malloc() and the difference between them ...

what does (char*)malloc(n) mean ??
Regards,
Rocky.
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Re: calloc and malloc function

 
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May 27th, 2009
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).
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Re: calloc and malloc function

 
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May 27th, 2009
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.
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Re: calloc and malloc function

 
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May 27th, 2009
From the C Standard:
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C Syntax (Toggle Plain Text) 
  1. 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) 
  1. 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.
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Re: calloc and malloc function

 
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May 27th, 2009
what do you mean in the last line ? can u please explain ?


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Originally Posted by BestJewSinceJC View Post
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.
Regards,
Rocky.
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Re: calloc and malloc function

 
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May 27th, 2009
calloc is essentially this:
c Syntax (Toggle Plain Text) 
  1. void *calloc ( size_t n, size_t size )
  2. {
  3.   void *base = malloc ( n * size );
  4.  
  5.   if ( base != NULL )
  6.     memset ( base, 0, n * size );
  7.  
  8.   return base;
  9. }
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.
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Re: calloc and malloc function

 
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May 27th, 2009
An obligatory link to http://c-faq.com/malloc/calloc.html
"One of the methods used by statists to destroy capitalism consists in establishing controls that tie a given industry hand and foot, making it unable to solve its problems, then declaring that freedom has failed and stronger controls are necessary." --Ayn Rand
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