FileHandling15.c

/*
 * C Program to Create Employee Record and Update it
 */
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#define size 200
 
struct emp
{
    int id;
    char *name;
}*emp1, *emp3;
 
void display();
void create();
void update();
 
FILE *fp, *fp1;
int count = 0;
 
void main(int argc, char **argv)
{
    int i, n, ch;
 
    printf("1] Create a Record\n");
    printf("2] Display Records\n");
    printf("3] Update Records\n");
    printf("4] Exit");
    while (1)
    {
        printf("\nEnter your choice : ");
        scanf("%d", &ch);
        switch (ch)
        {
        case 1:    
            fp = fopen(argv[1], "a");
            create();
            break;
        case 2:    
            fp1 = fopen(argv[1],"rb");
            display();
            break;
        case 3:    
            fp1 = fopen(argv[1], "r+");
            update();
            break;
        case 4: 
            exit(0);
        }
    }
}
 
/* To create an employee record */
void create()
{
    int i;
    char *p;
 
    emp1 = (struct emp *)malloc(sizeof(struct emp));
    emp1->name = (char *)malloc((size)*(sizeof(char)));
    printf("Enter name of employee : ");
    scanf(" %[^\n]s", emp1->name);
    printf("Enter emp id : ");
    scanf(" %d", &emp1->id);
    fwrite(&emp1->id, sizeof(emp1->id), 1, fp);
    fwrite(emp1->name, size, 1, fp);
    count++;   // count to number of entries of records
    fclose(fp);
}
 
/* Display the records in the file */
void display()
{    
    emp3=(struct emp *)malloc(1*sizeof(struct emp));    
    emp3->name=(char *)malloc(size*sizeof(char));
    int i = 1;
 
    if (fp1 == NULL)    
        printf("\nFile not opened for reading");
    while (i <= count)
    {
        fread(&emp3->id, sizeof(emp3->id), 1, fp1);
        fread(emp3->name, size, 1, fp1);
        printf("\n%d %s",emp3->id,emp3->name);
        i++;
    }
    fclose(fp1);
    free(emp3->name);
    free(emp3); 
}
 
void update()
{
    int id, flag = 0, i = 1;
    char s[size];
 
    if (fp1 == NULL)
    {
        printf("File cant be opened");
        return;
    }
    printf("Enter employee id to update : ");
    scanf("%d", &id);
    emp3 = (struct emp *)malloc(1*sizeof(struct emp));
        emp3->name=(char *)malloc(size*sizeof(char));
    while(i<=count)
    {    
        fread(&emp3->id, sizeof(emp3->id), 1, fp1);
        fread(emp3->name,size,1,fp1);
        if (id == emp3->id)
        {
            printf("Enter new name of emplyee to update : ");    
            scanf(" %[^\n]s", s);
            fseek(fp1, -204L, SEEK_CUR);
            fwrite(&emp3->id, sizeof(emp3->id), 1, fp1);
            fwrite(s, size, 1, fp1);
            flag = 1;
            break;
        }
        i++;
    }
    if (flag != 1)
    {
        printf("No employee record found");
        flag = 0;
    }
    fclose(fp1);
    free(emp3->name);        /* to free allocated memory */
    free(emp3);
}