Jan 23, 2011

C Program - struct usage example

This is a follow up post on my last blog update Pointers in C - an eye opener. The program touches on the following -
1. Using struct as Employee record
2. Using pointer to Employee* as an employee list
3. Using void pointer and casting it to an appropriate type to avoid duplicate code
4. Allocating memory and freeing memory

struct Person
{
    char *name;
    size_t age;
};
typedef struct Person Employee;

struct Organization
{
    Employee **emplist;
};
typedef struct Organization Org;

A sample execution of the program should be as shown:


The complete Program:
//File: StructExample.c

#include <stdio.h>

const size_t max_name_length  = 100;
size_t num_of_employees = 5;

struct Person
{
    char *name;
    size_t age;
};
typedef struct Person Employee;

struct Organization
{
    Employee **emplist;
};
typedef struct Organization Org;

void* allocate_memory(size_t size)
{
    void *ptr = (void *) malloc (size);
    if(NULL == ptr)
    {
        printf("\nERROR: Not enough memory");
        exit(-1);
    }
    return ptr;
}

Employee* get_new_employee()
{
    Employee *emp = (Employee*) allocate_memory(sizeof(Employee));
    return emp;
}

char* get_employee_name()
{
    char *str = (char*) allocate_memory(max_name_length);

    printf("Enter Employee Name: ");
    scanf("%s", str);
    return str;
}

size_t get_employee_age()
{
    size_t age;
    printf(" Enter Employee Age: ");
    scanf("%u", &age);
    return age;
}

Employee* get_employee()
{
    Employee *emp = get_new_employee();
    emp->name = get_employee_name();
    emp->age  = get_employee_age();
    return emp;
}

void print_employee(Employee *emp)
{
    printf("\n[Name]: %s", emp->name);
    printf("\n[Age] : %d", emp->age);
}

size_t get_employee_count()
{
    size_t empcount;
    printf("\nEnter Number of Employees: ");
    scanf("%u", &empcount);
    return empcount;
}

void get_org_employees(Org *org)
{
    size_t i;
    org->emplist = (Employee **) allocate_memory(sizeof(Employee) * num_of_employees);
    for(i = 0; i < num_of_employees; i++)
    {
        org->emplist[i] = get_employee();
    }
}

Org* get_new_org()
{
    Org* org = allocate_memory(sizeof(struct Organization));
    num_of_employees = get_employee_count();
    get_org_employees(org);
    return org;
}

void print_org(Org *org)
{
    size_t i;
    printf("\n[ORGANIZATION]");

    for(i = 0; i < num_of_employees; i++)
    {
        print_employee(org->emplist[i]);
    }
}

void delete_employee(Employee *emp)
{
    free(emp); emp = NULL;
}

void delete_org(Org *org)
{
    size_t i;
    for(i = 0; i < num_of_employees; i++)
    {
        delete_employee(org->emplist[i]);
    }
    free(org); org = NULL;
}

int main()
{
    Org *org = get_new_org();
    print_org(org);
    delete_org(org);
    return 0;
}

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