C Programs for dynamic memory allocations in C
/*code
for One Dimensional array dynamic memory allocaion*/
#include<stdio.h>
#include<stdlib.h>
#define
MAXSIZE 5
int
main()
{
int
*ptr;
ptr=(int
*)malloc(MAXSIZE*sizeof(int));
int i;
for(i=0;i<MAXSIZE;i++)
{
printf("ptr[%d]=%d
\n",i,i);
}
printf("\n");
return
0;
}
/*
ptr[0]=0
ptr[1]=1
ptr[2]=2
ptr[3]=3
ptr[4]=4
*/
/*
code
for 2 D alternate dynamic allocation
*/
#include<stdio.h>
#include<stdlib.h>
#define
MAXROW 3
#define
MAXCOLUMN 4
int
main()
{
int
*ptr,i,j;
ptr=(int
*)malloc(MAXROW*MAXCOLUMN*sizeof(int));
for(i=0;i<MAXROW;i++)
{
for(j=0;j<MAXCOLUMN;j++)
{
printf("%d+%d=(%d)
",i,j,i+j);
}
printf("\n");
}
printf("\n");
return
0;
}
/*
0+0=(0)
0+1=(1) 0+2=(2) 0+3=(3)
1+0=(1)
1+1=(2) 1+2=(3) 1+3=(4)
2+0=(2)
2+1=(3) 2+2=(4) 2+3=(5)
*/
/*
code
for 2-Dimensional array
*/
#include<stdio.h>
#include<stdlib.h>
#define
MAXROW 3
#define
MAXCOLUMN 4
int
main()
{
int
**ptr,i,j;
ptr=(int
**)malloc(MAXROW*sizeof(int
*));
for(i=0;i<MAXROW;i++)
{
ptr[i]=(int
*)malloc(MAXCOLUMN*sizeof(int
));
}
for(i=0;i<MAXROW;i++)
{
for(j=0;j<MAXCOLUMN;j++)
{
printf("%d+%d=(%d) ",i,j,i+j);
}
printf("\n");
}
return
0;
}
/*
0+0=(0)
0+1=(1) 0+2=(2) 0+3=(3)
1+0=(1)
1+1=(2) 1+2=(3) 1+3=(4)
2+0=(2)
2+1=(3) 2+2=(4) 2+3=(5)
*/
/*
dynamic
memory allocation for 3-Dimensinal array
*/
#include<stdio.h>
#include<stdlib.h>
#define
MAXX 2
#define
MAXY 3
#define
MAXZ 4
int
main()
{
int
***ptr,i,j,k;
ptr=(int
***)malloc(MAXX*sizeof(int
**));
for(i=0;i<MAXX;i++)
{
ptr[i]=(int
**)malloc(MAXX*sizeof(int
*));
for(j=0;j<MAXY;j++)
{
ptr[i][j]=(int *)malloc(MAXY*sizeof(int));
}
}
for(i=0;i<MAXX;i++)
{
for(j=0;j<MAXY;j++)
{
for(k=0;k<MAXZ;k++)
{
//printf("%d ",i);
printf("%d+%d+%d=(%d) ",i,j,k,i+j+k);
}
printf("\n");
}
printf("\n");
}
return
0;
}
/*
//when
i
0 0 0 0
0 0 0 0
0 0 0 0
1 1 1 1
1 1 1 1
1 1 1 1
//when
i+j+k
0+0+0=(0)
0+0+1=(1) 0+0+2=(2) 0+0+3=(3)
0+1+0=(1)
0+1+1=(2) 0+1+2=(3) 0+1+3=(4)
0+2+0=(2)
0+2+1=(3) 0+2+2=(4) 0+2+3=(5)
1+0+0=(1)
1+0+1=(2) 1+0+2=(3) 1+0+3=(4)
1+1+0=(2)
1+1+1=(3) 1+1+2=(4) 1+1+3=(5)
1+2+0=(3)
1+2+1=(4) 1+2+2=(5) 1+2+3=(6)
*/
….
-----
/*
code
for dynamic memory allocation for structure
*/
#include<stdio.h>
#include<stdlib.h>
struct
node
{
int
empid;
char
*name;
};
int
main()
{
struct
node *newnode;
newnode=(struct
node *)malloc(sizeof(struct node));
newnode->name=(char
*)malloc(sizeof(30));
newnode->empid=1020;
newnode->name="Aditya";
printf("\nempid=%d
and name=%s\n\n",newnode->empid,newnode->name);
newnode->empid=1021;
newnode->name="Birla";
printf("\nempid=%d
and name=%s\n\n",newnode->empid,newnode->name);
return
0;
}
/*
empid=1020
and name=Aditya
empid=1021
and name=Birla
*/
/*
code
Showing PROBLEM of returning local array address and solution
1.
static array
2.
dynamic memory alllocation
*/
#include<stdio.h>
#include<stdlib.h>//malloc
#include<string.h>//strcpy
char*
func1();
char*
func11();
char*
func2();
int
main()
{
char
*ptr1;
ptr1=func1();
printf("func1
returnd: %s\n",ptr1);//prints some GARBAGE as array of func1 was
local/auto
char
*ptr11;
ptr11=func11();
printf("func11
returnd: %s\n",ptr11);//prints Hello India11
char
*ptr2;
ptr2=func2();
printf("func2
returnd: %s\n",ptr2);//prints Hello India 2
printf("\n\n");
return
0;
}
/*PROBLEM
with returning local array*/
char*
func1()
{
char
buff1[20];//local array
//buff1="Hello
India1";/*error:incompatible types when assigning to type
âar[20]ârom type âar *â*/
strcpy(buff1,"HEllo
India1");//warning
return
(buff1);//warning returning local array is not ok
}
/*SOLUTION
1: use static array*/
char*
func11()
{
static
char buff11[20];//istatic local array
strcpy(buff11,"HEllo
India11");//warning
return
(buff11);//returning static local array is okay
}
/*SOLUTION
2: dynamic memory allocation*/
char*
func2()
{
char
*buff2;
buff2=(char
*)malloc(20);
buff2="Hello
India2";
return
(buff2);/*returning dynamically allocated memory is okay*/
}
/*
func1
returnd: á/c· ú¿
func11
returnd: HEllo India11
func2
returnd: Hello India2
*/
/*
Difference
between:
1.
char p1[5] //Array of characters
2.
char* p2[5] //Array of character pointers
3.
char (*p3)[5] //Pointer to Array of character
*/
#include<stdio.h>
#include<stdlib.h>
#include<string.h>
int
main()
{
int
*ptr[10];//ptr is array of 10 integer pointers
printf("\nptr[0]=%p\n",ptr[0]);//0x8049ff4
int
arr[10]={0,1,2,3,4,5,6,7,8,9};
//assgining
ptr[0] with the address of arr[0]
*ptr=arr;
//*ptr=arr[0];//warning: assignment makes pointer from
integer without a cast
printf("\n
ptr[0]=%p \n arr[0]=%p\n",ptr[0],arr);//0x8049ff4
/*with
characters */
char
p1[5];//p1 is 5-element array of chars
char
*p2[5];// p2 is 5-element array of char *
char
(*p3)[5];//p3 is pointer to 5-element array of chars
strcpy(p1,
"Hello");
p2[0]
= (char *) malloc(5 * sizeof(char));
strcpy(p2[0],
"India is Great");
p3
= &p1;
printf("\n
p1 = %s\np2[0] = %s\np3 = %s\n", p1, p2[0], *p3);
printf("\n");
return
0;
}
/*
___________
p1
|h| e | l | l | o |
---------------
"adi"
"mahi" "soni" "jaya" "bangalore"
^ ^ ^ ^ ^
|
| | | |
____________________________________
|0x9999|0x7777|0x3333|0x2222|0x6666|
|___0__|___1__|___2__|___3__|___4__|
p2
________
_____________________
|0x7777|
-------> | H | e | l | l | o |
|______|
|_0_|_1_|_2_|_3_|_4_|
p3
^
|
0x7777
*/
/*
ptr[0]=0xb7765fdc
ptr[0]=0xbfe81c34
arr[0]=0xbfe81c34
p1 =
Hello
p2[0] =
India is Great
p3 =
Hello
*/
