I’ve got a phonebook app that I’ve been trying to add malloc to over the last few days, but since I’m new to C and the book I have doesn’t go into the detail I would like, I’m not sure of all the tricks. Is it possible to use malloc when the user inputs information, and then use free() as a way to delete user input when the user elects to delete an individual from the phonebook? Right now regardless of whether I use free() or not, after the user deletes an entry and then tries to check the phonebook, the program crashes. I’m assuming(but we know what that means) that it has something to do with improperly freeing or not freeing the memory. Here is the code.
#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#include <conio.h>
#define BUFFER 50
//Structure for contacts
typedef struct friends_contact{
char *First_Name;
char *Last_Name;
char *home;
char *cell;
}fr;
//Function declarations
void menu(fr*friends ,int* counter,int user_entry,int i,char newbuddy[]);
void setFirst(fr*,int *,int i,char newbuddy[]);
char getFirst(fr*,int i);
void setLast(fr*friends, int* counter, int i,char newbuddy[]);
char getLast(fr*friends , int i);
void setHome(fr*friends, int* counter, int i,char newbuddy[]);
char getHome(fr*friends, int i);
void setCell(fr*friends, int* counter, int i,char newbuddy[]);
char getCell(fr*friends, int i);
void add_contact(fr*friends,int* counter,int i,char newbuddy[]);
void print_contact(fr*friends ,int* counter, int i);
char delete_contact(fr*friends ,int* counter, int i);
char show_contact(fr*friends ,int* counter, int i);
int main() {
int user_entry=0;
fr friends[5];
char newbuddy[BUFFER];
int counter=0;
int i=0;
menu(friends, &counter,user_entry,i,newbuddy);
getch();
return 0;
}
//Menu function
void menu(fr*friends,int* counter,int user_entry, int i,char newbuddy[]) {
do{
int result;
printf("\nPhone Book Application\n");
printf("1) Add friend\n2) Delete friend\n3) Show a friend\n4) Show phonebook\n5)Exit\n");
scanf("%d", &user_entry);
if(user_entry==1)
{
add_contact(friends,counter,i,newbuddy);
}
if(user_entry==2)
{
delete_contact(friends ,counter,i);
}
if(user_entry==3)
{
result=show_contact(friends ,counter,i);
if(result==0){
printf("\nName not Found\n");
}else{
result;
}
}
if(user_entry==4)
{
print_contact(friends, counter,i);
}
}while(user_entry!=5);
}
//Start of Set functions. Each entry has its own set function that gathers the data
void setFirst(fr*friends, int* counter, int i,char newbuddy[]) {
printf("Enter a first name \n");
scanf("%s",newbuddy);
friends[*counter].First_Name=malloc(BUFFER*strlen(newbuddy));
strcpy(friends[*counter].First_Name, newbuddy);
}
void setLast(fr*friends, int* counter, int i,char newbuddy[]) {
printf("Enter a last name \n");
scanf("%s",newbuddy);
friends[*counter].Last_Name=malloc(BUFFER*strlen(newbuddy));
strcpy(friends[*counter].Last_Name, newbuddy);
}
void setHome(fr*friends, int* counter, int i,char newbuddy[]) {
printf("Enter a home number \n");
scanf("%s",newbuddy);
friends[*counter].home=malloc(BUFFER*strlen(newbuddy));
strcpy(friends[*counter].home, newbuddy);
}
void setCell(fr*friends, int* counter, int i,char newbuddy[]) {
printf("Enter a cell number \n");
scanf("%s",newbuddy);
friends[*counter].cell=malloc(BUFFER*strlen(newbuddy));
strcpy(friends[*counter].cell, newbuddy);
}
//Start of Get functions. Each function sends the data to the executing function.
char getFirst(fr*friends , int pos) {
printf("%s ", friends[pos].First_Name);
return *friends[pos].First_Name;
}
char getLast(fr*friends , int pos) {
printf("%s\n", friends[pos].Last_Name);
return *friends[pos].Last_Name;
}
char getHome(fr*friends , int pos) {
printf("(Home) ""%s\n", friends[pos].home);
return *friends[pos].home;
}
char getCell(fr*friends , int pos) {
printf("(Cell) ""%s\n", friends[pos].cell);
return *friends[pos].cell;
}
//This function allows for the all the set functions to be added.
void add_contact(fr*friends,int* counter,int i,char newbuddy[]) {
setFirst(friends,counter,i,newbuddy);
setLast(friends,counter,i,newbuddy);
setHome(friends,counter,i,newbuddy);
setCell(friends,counter,i,newbuddy);
(*counter)++;
}
//This is used to delete a name out of the book.
char delete_contact(fr*friends ,int* counter, int i)
{
char name_search[50]={'\0'};
char Delete[5]={'\0'};
printf("Search by last name\n");
scanf("%s",name_search);//Name entry
for(i=0;i<*counter;i++)
{
if(strcmp(name_search,friends[i].Last_Name)==0)//Copys over the name entered
{
strcpy(friends[i].Last_Name,Delete);
(*counter)++;
printf("\nName has been deleted\n");
}
}
}
//This function prints out all the contact information
void print_contact(fr*friends ,int* counter, int i) {
for( i = 0; i < *counter; i++)
if (strlen(friends[i].First_Name) && strlen(friends[i].Last_Name)&& strlen(friends[i].home)&& strlen(friends[i].cell ))
{
getFirst(friends, i);
getLast(friends, i);
getHome(friends, i);
getCell(friends, i);
}
}
//Displays the contact in which you are searching for.
char show_contact(fr*friends ,int* counter, int i)
{
char name_search2[50]={'\0'};
printf("Please enter a last name\n");
scanf("%s",name_search2);
for(i=0;i<*counter;i++)
{
//If the name is found, it reaturns the contact info.
if(strcmp(name_search2,friends[i].Last_Name)==0)
{
return printf("%s " "%s" "(Home)""%s""(Cell)" "%s\n",friends[i].First_Name, friends[i].Last_Name,friends[i].home,friends[i].cell);
}
}
return 0;
}
I didn’t add the free() code because regardless it seemed to be getting the same results. Why would the program crash only after I have deleted a name from the list?
Step1: Isolating the issue:
Step2: Possible Problem
This is executed, when the name to be deleted is found. Why would you increment the count of all names in the list? I think this should be a decrement instead, or shouldn’t be done within the loop at all.