In software engineering, a memory allocation library is a set of routines for allocating and freeing blocks of memory, commonly used for dynamic memory allocation. These libraries are sometimes called allocators or allocator libraries. They allow programmers to create and manage objects dynamically without worrying about the size of allocated blocks or the amount of available memory.
In C programming, the standard library provides three different memory allocation routines: calloc, malloc, and realloc. The calloc routine allocates and initializes an array of pointers; the malloc routine allocates memory for a block of bytes, and the really routine changes the size of an existing block.
These functions are part of the standard C library. However, they are not generally considered part of the C++ standard library.
For memory allocation in C++, the Standard Template Library provides two classes: std::allocator and std::vector. Both of these classes are derived from std::allocator. The difference between the two is that std::vector uses contiguous storage and does not provide means of reallocation while std::allocator does.
The most important advantage of using a memory allocation library is that it provides a consistent interface for allocating and deallocating memory. This is especially useful when developing a library or framework, where you need to be sure that all of your objects are allocated with the same allocator.
Calloc, malloc, and realloc are all members of the C standard library. C++ includes a class named std::allocator, which is a base class for both the standard allocator and the STL allocator.
Malloc vs Calloc: The best C memory allocation library for malloc?
The first difference can be found in the definition of both terms. Malloc is used to mean memory allocation while calloc refers to contiguous allocation. In addition, Malloc is said to accommodate a single argument at a time which must be number of byte. That is contrary to calloc which has the capacity of taking two arguments at a go. Arguments associated with calloc are primarily number of blocks as well as the size of each and every block.
Another difference between malloc c vs calloc is the where the pointer is usually returned to. For malloc, the pointer is sent back to the bytes of uninitialized storage. However, when malloc assigns a space and it happens to overrun, the final outcomes become undefined. Calloc on the other hand the pointer is returned to enough space set free for the task. To add on that, byte storage is primarily initialized to zero.
Extended research in the field of programming proves that the malloc is faster than calloc. The reason behind calloc taking much time compared to that taken by malloc is of the extraction process. It is time-consuming due to the initializing of allocated memory. At times the difference seems to be unrecognizable as both may take longer.
Indeed, malloc and calloc are used in C programming but have differences in dynamic memory allocation. The unique features in both facilitate their ability to develop data as well as structures of programs. Therefore, understanding the major differences helps the user understand the language and syntax used when formulating program codes. What matters most is to note the difference in allocation and storage of memory bytes in malloc as well as calloc. In case memory allocation is not successful, a null pointer is returned to indicate a decline in that process.
Calloc() Function
The calloc() function allocates memory for an array of objects. This function is similar to the malloc() function. It differs in how memory is allocated. The calloc() function allocates memory in blocks of a specified size. On the other hand, malloc() allocates memory in chunks of a specified size. This is the reason why the calloc() function takes only one argument. While the malloc() function takes three arguments. Let’s see how these two functions are implemented.
The calloc() function is implemented as follows
void *calloc(size_t count, size_t size) {
void *p = malloc(count*size);
if (!p) return NULL;
return memset(p, 0, count*size);
}
The calloc() function is called like this
int main() {
int *a, *b;
a = calloc(10, sizeof(*a));
b = calloc(20, sizeof(*b));
printf("%d %d\n", sizeof(*a), sizeof(*b));
free(a);
free(b);
return 0;
}
The calloc() function is a bit faster than the malloc(). In fact, the calloc() function is equivalent to the malloc() function. However, the calloc() function does not have the ability to check if the memory is freed properly. So, it is not recommended to use the calloc() function.
The calloc() function allocates memory for an array of M integers. It is a function for the allocation of arrays. So, it can be used to allocate memory for a multidimensional array.
Calloc is used to allocate memory for the following purposes.
- Allocate memory for arrays
- Allocate memory for structures
- Allocate memory for linked lists
Malloc() Function
Malloc() is a function to allocate memory. The malloc() function has the following prototype.
void *malloc(size_t size)
This function can be used as follows.
int *a, *b;
a = malloc(20*sizeof(*a));
b = malloc(40*sizeof(*b));
printf("%d %d\n", sizeof(*a), sizeof(*b));
free(a);
free(b);
return 0;
The malloc() function can be used to allocate any type of memory. For example, it can allocate memory to store double values.
The malloc() function has the following prototype.
void *malloc(size_t size);
This function has two arguments. The first argument is the size of the block of memory that needs to be allocated. The second argument is the type of memory that is required to be allocated.
The malloc() function is implemented as follows.
void *malloc(size_t size) {
void *p = malloc(size);
if (!p) abort();
return p;
}
Now, let’s see the calloc() function in action.
#include
#include
#define M 10
int main()
{
int i[M];
for (int i = 0; i < M; i++)
{
printf("%d", i);
i++;
}
// Calling calloc
int *a, *b;
a = calloc(M, sizeof(*a));
b = calloc(M, sizeof(*b));
// Checking if memory is correctly allocated
printf("%d %d\n", sizeof(*a), sizeof(*b));
// Freeing the memory
free(a);
free(b);
return 0;
}
Important differences – calloc() vs malloc() functions
Calloc and malloc are very similar in how they work. In fact, they are almost identical in implementation. Both of them can be used to allocate memory. So, you need to choose the one that suits your purpose. The calloc() function allocates memory in blocks of a specified size. So, it is suitable for allocating memory for arrays. On the other hand, the malloc() function allocates memory in chunks of a specified size. So, it is suitable for allocating memory for structures. Calloc() and Malloc() are used to allocate memory for different types of data.
Malloc() – The malloc() function allocates memory and returns a pointer to the beginning of the allocated buffer. malloc(3) allocates 3 bytes of memory. The allocated memory is 0x00000000.
- When you calloc(), the allocated memory is filled with zeros. However, you can use the free() function to free the memory.
Calloc() – The calloc() function allocates memory and copies its contents from an array of a given size. The first argument is the number of elements to allocate. The second argument is the size of the allocated buffer in bytes. Calloc(3, 3) allocates three elements of size 3 bytes. The allocated memory is 0x00000000.
- When you malloc(), the allocated memory is not zeroed. So, you have to fill the memory yourself.
In conclusion, for a general-purpose application, calloc() is preferred over malloc() for two reasons:First, you can only allocate a specific number of elements with calloc(). Second, calloc() allocates memory in a block of contiguous bytes. So if you calloc() a single number of elements, your memory allocation will be contiguous. Also, calloc() returns NULL on error, whereas malloc() doesn’t return NULL on error. Finally, when a variable is declared as char *p = calloc(sizeof(char)); it is initialized to NULL on allocation. And since calloc() can allocate blocks of memory, you can easily pass pointers to a block of memory to functions that require a pointer to a character.
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