C/Memory/Memory Allocation

Allocate array in memory: how to use calloc

<source lang="cpp">

1. include <stdio.h>
2. include <stdlib.h>

int main () {

 int i, n;
 int *pointerData;
 printf ("Enter number of items to be stored: ");
 scanf ("%d", &i);
 pointerData = (int*) calloc (i, sizeof(int));
 
 if (pointerData==NULL) 
     exit (1);
     
 for (n = 0; n < i; n++)
 {
   printf ("Enter number #%d: ", n);
   scanf ("%d", &pointerData[ n ]);
 }
 printf ("You have entered: ");
 
 for (n = 0; n < i; n++) 
     printf ("%d ", pointerData[ n ]);
 free (pointerData);
 return 0;

}

      </source>

Allocate memory

<source lang="cpp">

1. include <stdlib.h>
2. include <stdio.h>

int main() {

 float *p;
 p = calloc(100, sizeof(float));
 if(!p) {
   printf("Allocation Error\n");
   exit(1);
 }
 return 0;

}

      </source>

Allocate memory and reallocate

<source lang="cpp">

1. include <stdlib.h>
2. include <stdio.h>
3. include <string.h>

int main(void) {

 char *p;
 p = malloc(17);
 if(!p) {
   printf("Allocation Error\n");
   exit(1);
 }
 strcpy(p, "This is 16 chars");
 p = realloc(p, 18);
 if(!p) {
   printf("Allocation Error\n");
   exit(1);
 }
 strcat(p, ".");
 printf(p);
 free(p);
 return 0;

}

      </source>

Allocate memory block: how to use malloc

<source lang="cpp">

1. include <stdio.h>
2. include <stdlib.h>

int main () {

 int i, n;
 char *str;
 printf ("String Length? ");
 scanf ("%d", &i);
 str = (char*) malloc (i+1);
 if (str == NULL) 
     exit (1);
 for ( n = 0; n < i; n++)
     str[n] = rand() % 26 + "a";
 
 str[i] = "\0";
 printf ("Random string: %s\n", str);
 free (str);
 return 0;

}

      </source>

Allocate space for a string dynamically, request user input, and then print the string backwards

<source lang="cpp">

1. include <stdlib.h>
2. include <stdio.h>
3. include <string.h>

int main(void) {

 char *s;
 register int i;
 s = malloc(80);
 if(!s) {
   printf("Memory request failed.\n");
   exit(1);
 }
 gets(s);
 for(i = strlen(s) - 1; i >= 0; i--) 
     putchar(s[ i ]);
 free(s);
 return 0;

}

      </source>

Find out the address after malloc

<source lang="cpp">

1. include <stdio.h>
2. include <malloc.h>

main() {

   int  *base;
   int i,j;
   int cnt = 3;
   int sum = 0;

   base = (int *)malloc(cnt * sizeof(int));
   printf("the base of allocation is %16lu \n",base);
   if(!base)
       printf("unable to allocate size \n");
   else {
     for(j = 0;j < cnt; j++)
         *(base+j)=5;
   }
   for(j = 0;j < cnt; j++)
     sum = sum + *(base+j);
   printf("total sum is %d\n",sum);
   free(base);
   printf("the base of allocation is %16lu \n",base);
   base = (int *)malloc(cnt * sizeof(int));
   printf("the base of allocation is %16lu \n",base);
   free(base);
   base = (int *)calloc(10,2);
   printf("the base of allocation is %16lu \n",base);
   free(base);

}

      </source>

Get the current system free memory

<source lang="cpp">

1. include <stdio.h>
2. include <stdlib.h>

int main(void) {

 char *p;
 long l;
 l = 0;
 do {
   p = malloc(1000);
   if(p) 
       l += 1000;
 } while(p);
 printf("Approximately %ld bytes of free memory.", l);
 return 0;

}

      </source>

Reallocate memory block: how to use realloc

<source lang="cpp">

1. include <stdio.h>
2. include <stdlib.h>

int main () {

 int input, n;
 int count=0;
 int *numbers = NULL;
 do {
    printf ("Enter an integer value ( enter 0 to stop): ");
    scanf ("%d", &input);
    count++;
    numbers = (int*) realloc (numbers, count * sizeof(int));
    if (numbers == NULL) { 
        puts ("Error (re)allocating memory"); 
        exit ( 1 ); 
    }
    numbers[ count - 1 ] = input;
 } while (input!=0);
 printf ("Numbers entered: ");
 
 for ( n = 0; n < count; n++) 
     printf ("%d ",numbers[ n ]);
     
 free (numbers);
 return 0;

}

      </source>

Store string in allocated memory

<source lang="cpp">

1. include <stdlib.h>
2. include <stdio.h>

int main(void) {

 char *str[100];
 int i;
 for(i = 0; i < 100; i++) {
   if((str[i] = malloc( 128 )) == NULL) {
     printf("Allocation Error\n");
     exit(1);
   }
   gets(str[i]);
 }
 /* now free the memory */
   
 for(i = 0; i < 100; i++) 
     free(str[i]);
 return 0;

}

      </source>

Use malloc to allocate memory

<source lang="cpp">

1. include <stdio.h>
2. include <stdlib.h>

int main(void) {

 char *p;
 p = malloc(80);
 if( !p ) {
   printf("Memory Allocation Failed");
   exit(1);
 }
 printf("Enter a string: ");
 gets( p );
 
 printf( p );
 free( p );
 return 0;

}

      </source>