C Tutorials
| Memory Management |
The C programming language provides several functions for memory allocation and management. These functions can be found in the <stdlib.h> header file.
| S.N. | Function and Description |
|---|---|
| 1 | void *calloc(int num, int size); This function allocates an array of num elements each of which size in bytes will be size. |
| 2 | void free(void *address); This function release a block of memory block specified by address. |
| 3 | void *malloc(int num); This function allocates an array of num bytes and leave them initialized. |
| 4 | void *realloc(void *address, int newsize); This function re-allocates memory extending it upto newsize. |
| Allocating Memory Dynamically |
While doing programming, if you are aware about the size of an array, then it is easy and you can define it as an array. For example to store a name of any person, it can go max 100 characters so you can define something as follows:
char name[100];
But now let us consider a situation where you have no idea about the length of the text you need to store, for example you want to store a detailed description about a topic. Here we need to define a pointer to character without defining how much memory is required and later based on requirement we can allocate memory as shown in the below example:
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
int main()
{
char name[100];
char *description;
strcpy(name, "Wind T");
/* allocate memory dynamically */
description = malloc( 200 * sizeof(char) );
if( description == NULL )
{
fprintf(stderr, "Error - unable to allocate required memory\n");
}
else
{
strcpy( description, "Wind Trainers is a Tutorial Website ");
}
printf("Name = %s\n", name );
printf("Description: %s\n", description );
}
| Resizing and Releasing Memory |
When our program comes out, operating system automatically release all the memory allocated by our program but as a good practice when you are not in need of memory anymore then we should release that memory by calling the function free().
Alternatively, we can increase or decrease the size of an allocated memory block by calling the function realloc(). Let us check the above program once again and make use of realloc() and free() functions:
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
int main()
{
char name[100];
char *description;
strcpy(name, "Wind T");
/* allocate memory dynamically */
description = malloc( 30 * sizeof(char) );
if( description == NULL )
{
fprintf(stderr, "Error - unable to allocate required memory\n");
}
else
{
strcpy( description, "Wind Trainers.");
}
/* suppose you want to store bigger description */
description = realloc( description, 100 * sizeof(char) );
if( description == NULL )
{
fprintf(stderr, "Error - unable to allocate required memory\n");
}
else
{
strcat( description, "Wind Trainers - Online Training ");
}
printf("Name = %s\n", name );
printf("Description: %s\n", description );
/* release memory using free() function */
free(description);
}
|
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