UNIT 3
void pointer(general purpose pointer) can be used to store address of any varible.
wild pointers are pointers which are not initialised and store garbage value . to error aa skta hai .
>>
#include<stdio.h>
struct Employee
{
int Id;
char Name[25];
int Age;
long Salary;
};
void Display(struct Employee*);
int main()
{
struct Employee Emp = {2,"ram",28,35000};
Display(&Emp);
}
void Display(struct Employee *E)
{
printf("\n\nEmployee Id : %d",E->Id);
printf("\nEmployee Name : %s",E->Name);
printf("\nEmployee Age : %d",E->Age);
printf("\nEmployee Salary : %ld",E->Salary);
}
>>
#include<stdio.h>
struct Employee
{
int Id;
char Name[25];
int Age;
long Salary;
};
Employee Input(); //Statement 1
int main()
{
struct Employee Emp;
Emp = Input();
printf("\n\nEmployee Id : %d",Emp.Id);
printf("\nEmployee Name : %s",Emp.Name);
printf("\nEmployee Age : %d",Emp.Age);
printf("\nEmployee Salary : %ld",Emp.Salary);
}
Employee Input()
{
struct Employee E;
printf("\nEnter Employee Id : ");
scanf("%d",&E.Id);
printf("\nEnter Employee Name : ");
scanf("%s",&E.Name);
printf("\nEnter Employee Age : ");
scanf("%d",&E.Age);
printf("\nEnter Employee Salary : ");
scanf("%ld",&E.Salary);
return E; //Statement 2
}
#include <stdio.h>
//Structure declartion
struct employee {
char name[40];
int empid;
int experience;
}emp;
void displaydetails(struct employee*); //function declaration
int main()
{
struct employee *empptr; //pointer declaration
empptr = &emp; //initial
printf("\nEnter the name of the Employee : ");
scanf("%s", empptr->name);
printf("\nEnter the Employee Id : ");
scanf("%d",&empptr->empid);
printf("\nEnter Experience of the Employee : ");
scanf("%d",&empptr->experience);
displaydetails(empptr);
return 0;
}
//Function Definition
void displaydetails(struct employee *empptr)
{
printf("\n---------Details List--------- \n ");
printf("Employee Name : %s",empptr->name);
printf("\nEmployee ID : %d ",empptr->empid);
printf("\nEmployee Experience : %d ",empptr->experience);
}
>>
#include<stdio.h>
struct team {
char *name;
int members;
char captain[20];
}
t1 = {"India",11,"Dhoni"} , *sptr = &t1;
int main()
{
printf("\nTeam : %s",(*sptr).name);
printf("\nMemebers : %d",sptr->members);
printf("\nCaptain : %s",(*sptr).captain);
return 0;
}
>>
>> DMA is used to increase orr decrease size of array or to allocate memory.
- A Pointer is the only way to access Dynamic Memory Allocation.
>> malloc() memory allocation
#include <stdio.h>
#include <stdlib.h>
int main()
{
int n, i, *ptr, sum = 0;
printf("Enter number of elements: ");
scanf("%d", &n);
ptr = (int*) malloc(n * sizeof(int));
// if memory cannot be allocated
if(ptr == NULL)
{
printf("Error! memory not allocated.");
exit(0);
}
printf("Enter elements: ");
for(i = 0; i < n; ++i)
{
scanf("%d", ptr + i);
sum += *(ptr + i);
}
printf("Sum = %d", sum);
return 0;
}
>>calloc() -- contagious allocation
#include <stdio.h>
#include <stdlib.h>
int main()
{
int n, i, *ptr, sum = 0;
printf("Enter number of elements: ");
scanf("%d", &n);
ptr = (int*) calloc(n, sizeof(int));
if(ptr == NULL)
{
printf("Error! memory not allocated.");
exit(0);
}
else{
printf("Enter elements: ");
for(i = 0; i < n; ++i)
{
scanf("%d", ptr + i);
sum += *(ptr + i);
}
printf("Sum = %d", sum);}
return 0;
}
>>difference between calloc and malloc is that the memory that is allocated by calloc is initialized with 0.
and calloc take 2 arguments and malloc take 1.
>>Malloc() and calloc() both functions return void* (a void pointer), to use/capture the returned value in pointer variable we convert it's type.
>>
Example: Program to Represent the reallocation in memory using realloc().
#include <stdio.h>
#include <stdlib.h>
int main()
{
// This pointer will hold the
// base address of the block created
int* ptr;
int n, i;
// Get the number of elements for the array
n = 5;
printf("Enter number of elements: %d\n", n);
// Dynamically allocate memory using calloc()
ptr = (int*)calloc(n, sizeof(int));
// Check if the memory has been successfully
// allocated by malloc or not
if (ptr == NULL) {
printf("Memory not allocated.\n");
exit(0);
}
else {
// Memory has been successfully allocated
printf("Memory successfully allocated using calloc.\n");
// Get the elements of the array
for (i = 0; i < n; ++i) {
ptr[i] = i + 1;
}
// Print the elements of the array
printf("The elements of the array are: ");
for (i = 0; i < n; ++i) {
printf("%d, ", ptr[i]);
}
// Get the new size for the array
n = 10;
printf("\n\nEnter the new size of the array: %d\n", n);
// Dynamically re-allocate memory using realloc()
ptr = realloc(ptr, n * sizeof(int));
// Memory has been successfully allocated
printf("Memory successfully re-allocated using realloc.\n");
// Get the new elements of the array
for (i = 5; i < n; ++i) {
ptr[i] = i + 1;
}
// Print the elements of the array
printf("The elements of the array are: ");
for (i = 0; i < n; ++i) {
printf("%d, ", ptr[i]);
}
}
return 0;
}
>>
C free()
free method in C is used to dynamically de-allocate the memory. The memory allocated using functions malloc() and calloc() is not de-allocated on their own. Hence the free() method is used, whenever the dynamic memory allocation takes place. It helps to reduce wastage of memory by freeing it.
Syntax:
free(ptr);
Example : Program to demonstrate free() in C.
#include <stdio.h>
#include <stdlib.h>
int main()
{
// This pointer will hold the
// base address of the block created
int *ptr, *ptr1;
int n, i;
// Get the number of elements for the array
n = 5;
printf("Enter number of elements: %d\n", n);
// Dynamically allocate memory using malloc()
ptr = (int*)malloc(n * sizeof(int));
// Dynamically allocate memory using calloc()
ptr1 = (int*)calloc(n, sizeof(int));
// Check if the memory has been successfully
// allocated by malloc or not
if (ptr == NULL || ptr1 == NULL) {
printf("Memory not allocated.\n");
exit(0);
}
else {
// Memory has been successfully allocated
printf("Memory successfully allocated using malloc.\n");
// Free the memory
free(ptr);
printf("Malloc Memory successfully freed.\n");
// Memory has been successfully allocated
printf("\nMemory successfully allocated using calloc.\n");
// Free the memory
free(ptr1);
printf("Calloc Memory successfully freed.\n");
}
return 0;
}
>> 1d array using pointer
#define FAIL 1
#define TRUE 0
int main(int argc, char*argv[])
{
int *piBuffer = NULL; //pointer to integer
int nBlock = 0; //Variable store number ofblock
int iLoop = 0; //Variable for looping
printf("\nEnter the number of block =");
scanf("%d",&nBlock); //Getinput for number of block
piBuffer = (int *)malloc(nBlock *sizeof(int));
//Check memory validity
if(piBuffer == NULL)
{
return FAIL;
}
//copy iLoop to each block of 1D Array
for (iLoop =0; iLoop < nBlock; iLoop++)
{
piBuffer[iLoop] = iLoop;
}
//Print the copy data
for (iLoop =0; iLoop < nBlock; iLoop++)
{
printf("\npcBuffer[%d] =%d\n", iLoop,piBuffer[iLoop]);
}
// free allocated memory
free(piBuffer);
return TRUE;
}
Using a single pointer:
int main()
{
int r = 3, c = 4;
int *arr = (int *)malloc(r * c *sizeof(int));
int i, j, count = 0;
for(i = 0; i < r; i++)
for (j = 0; j < c; j++)
*(arr + i*c + j) = ++count;
for (i = 0; i < r; i++)
for (j = 0; j < c; j++)
printf("%d ", *(arr + i*c +j));
/* Code for further processing and freethe
dynamically allocated memory */
return 0;
}
Using an array of pointers
int main()
{
int r = 3, c = 4, i, j, count;
int *arr[r];
for (i=0; i<r; i++)
arr[i] = (int *)malloc(c *sizeof(int));
// Note that arr[i][j] is same as*(*(arr+i)+j)
count = 0;
for (i = 0; i < r; i++)
for (j = 0; j < c; j++)
arr[i][j] = ++count; // Or*(*(arr+i)+j) = ++count
for (i = 0; i < r; i++)
for (j = 0; j < c; j++)
printf("%d ", arr[i][j]);
/* Code for further processing and freethe
dynamically allocated memory */
return 0;
}
Using pointer to a pointer
int main()
{
int r = 3, c = 4, i, j, count;
int **arr = (int **)malloc(r * sizeof(int*));
for (i=0; i<r; i++)
arr[i] = (int *)malloc(c *sizeof(int));
// Note that arr[i][j] is same as*(*(arr+i)+j)
count = 0;
for (i = 0; i < r; i++)
for (j = 0; j < c; j++)
arr[i][j] = ++count; // OR *(*(arr+i)+j) = ++count
for (i = 0; i < r; i++)
for(j = 0; j < c; j++)
printf("%d ", arr[i][j]);
/* Code for further processing and freethe
dynamically allocated memory */
return 0;
}
Using double pointer and one malloc call
int main()
{
int r=3, c=4, len=0;
int *ptr, **arr;
int count = 0,i,j;
len = sizeof(int *) * r + sizeof(int) * c* r;
arr = (int **)malloc(len);
// ptr is now pointing to the first elementin of 2D array
ptr = (int *)(arr + r);
// for loop to point rows pointer toappropriate location in 2D array
for(i = 0; i < r; i++)
arr[i] = (ptr + c * i);
for (i = 0; i < r; i++)
for (j = 0; j < c; j++)
arr[i][j] = ++count; // OR *(*(arr+i)+j)= ++count
for (i = 0; i < r; i++)
for (j = 0; j < c; j++)
printf("%d ", arr[i][j]);
return 0;
}
>>memory allocation to sturcture
#include <stdio.h>
#include <stdlib.h>
struct course {
int marks;
char subject[30];
};
int main() {
struct course *ptr;
int i, noOfRecords;
printf("Enter the number of records: ");
scanf("%d", &noOfRecords);
// Memory allocation for noOfRecords structures
ptr = (struct course *)malloc(noOfRecords * sizeof(struct course));
for (i = 0; i < noOfRecords; ++i) {
printf("Enter the name of the subject and marks respectively:\n");
scanf("%s %d", (ptr + i)->subject, &(ptr + i)->marks);
}
printf("Displaying Information:\n");
for (i = 0; i < noOfRecords; ++i)
printf("%s\t%d\n", (ptr + i)->subject, (ptr + i)->marks);
return 0;
}
Comments
Post a Comment