The C language gives us the possibility that a program can allocate and manage the memory in real time. For this purpose, there are the malloc(), calloc(), realloc(), and free() functions. The malloc() and calloc() functions allocate the dynamic memory. Although they both serve the same purpose, they have different properties that adapt them to the needs of each programmer.
In this Linux Ways article, we will look at these two functions and compare their syntax, calling method, and operation. This way, you can see the different methods where the C language can allocate the dynamic memory and which one best suits your needs.
Features of the Malloc() Function in the C Language
The malloc() function allocates the memory in real time. Let’s see the prototype of this function:
The malloc() function allocates a space of memory with the size in bytes that are specified in the size input argument and returns a void pointer to the memory space to access it.
This function can allocate the memory areas that are intended for the storage of all data types that are used in C. To do this, we must declare a pointer with the data type that we want to process in it and specify the total size in bytes in the input argument size that the allocated area contains.
Features of the Calloc() Function in the C Language
The calloc() function allocates the memory spaces in real time. Let’s see the prototype of this function:
The calloc() function allocates a memory location of size that consists of arrays of the size in bytes that are specified in the “nmemb” input argument and returns an empty pointer that points to the allocated memory location. This function assigns a value of 0 to all data that makes up the allocated memory space.
This calloc() function can allocate the memory locations for all data types that are used in C. To do this, we must declare the pointer that we use to access the memory with the type of data that we want to manage in it, and allocate a total memory location according to its type.
Malloc() vs Calloc() Function in the C Language
Now that we have given a brief overview of these two features, let’s look at their characteristics and compare them so that you can choose the one that best suits your needs.
Output arguments: Both functions return a pointer of type void so we can assign to it the type of data that we want to work with in the allocated memory area. This makes it possible to read and write the memory that is allocated by both functions with any data type that is used in C.
Input arguments: Although both functions have similarities, they differ in the way that they assign and organize the data in their input arguments.
The malloc() function uses only one input argument which specifies the size in bytes of the memory to allocate. This means that if we need to allocate a range of data consisting of integers, for example, we must perform an operation with the size of the data type multiplied by the memory size to be allocated. Let’s see how to allocate a size of 16 data of type int using the malloc() function:
As we can see, when specifying the size of the part to be allocated in bytes, we must perform an operation to determine the number of bytes that each data occupies since this depends on its type and the system on which the program is executed.
The calloc() function, on the other hand, uses two input arguments. The first is the size argument which specifies the amount of data to allocate in the space while “nmemb” specifies the size of each of that data.
At this point, the calloc() function seems to be the most practical since it specifies directly the size in bytes of the data to be allocated in the “nmemb” argument. However, when allocating the memory, we must take into account that certain types of data that vary their size depending on the system on which the program is running. For example, the data of type int occupies a size of 4 bytes in a 32-bit system, while it occupies 8 bytes in a 64-bit system.
This leads to the fact that we have to perform the “sizeof” operations in both functions to establish the size of certain data types. Let’s see how to allocate a size of 16 data of type int using the calloc() function:
As we can see, we need to perform the “sizeof” operations in both the malloc() and calloc() functions to allocate the specific data types in the memory space.
Conclusion
In this Linux Ways article, we compared the malloc() and calloc() functions, both of which come from the same set and serve the same purpose but have different properties.
In this comparison, we could see that the main difference between them is in their input arguments and in the way they allocate the size of the memory area to be allocated and how they organize the bytes.
We could also see that while the calloc() function has an input argument that specifies the size in bytes of the cells of the allocated memory space, this alone is not a practical method when the type of data that we want to allocate depends on the system on which the program is running.
Although the use of one function or another is up to the criteria and preferences of each programmer, the malloc() function, because of its simplicity, is most often used in programs that use the dynamic memory.
