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Error:Null Pointer assignment

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Join Date: Nov 2005

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comwizz

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Error:Null Pointer assignment

Jan 25th, 2006

Hello everyone,
I ahd to make a program for initializing members of a class and displaying them.The members were name , bank account no, account type and current balance.
Well , the program works well except for that null pointer assignment is displayed on the screen after correct output.Could you tell me a reason why this is happening?
Thanks,
comwizz.

 Help with Code Tags 
 C++ Syntax (Toggle Plain Text) 
/Program to deposit money in a bank account
#include<iostream.h>
#include<string.h>
#include<conio.h>
class account
{
 public:
 void initialize(char *p,int,char *c,float);
 void deposit(float);
 void withdraw(float);
 void display(void)
 {
 cout<<"Name: "<<p<<endl;
 cout<<"Balance: "<<balance<<endl;
 }
 private:
 float balance,principal;
 char *p,*account_type;
 int account_no;
};
void account::initialize(char *name,int acc_no,char *acc_type,float initial)
{
 int q=strlen(name);
 p=new char[q+1];
 strcpy(p,name);
 account_no=acc_no;
 account_type=acc_type;
 principal=initial;
 balance=initial;
}
void account::deposit(float add)
{
 balance=add+principal;
}
void account::withdraw(float subtract)
{
 balance=principal-subtract;
}
void main()
{
 int i,no;
 char *name,*acc_type;
 float initial;
 account s[2];
 for(i=0;i<2;i++)
 {
  cout<<"Enter name "<<i+1<<": "<<endl;
  cin>>name;
  cout<<"Enter account no :\n";
  cin>>no;
  cout<<"Enter account type: \n";
  cin>>acc_type;
  cout<<"Enter principal amount:\n";
  cin>>initial;
  s[i].initialize(name,no,acc_type,initial);
 }
 for(i=0;i<2;i++)
 {
  s[i].display();
 }
}
/Program to deposit money in a bank account
#include<iostream.h>
#include<string.h>
#include<conio.h>
class account
{
 public:
 void initialize(char *p,int,char *c,float);
 void deposit(float);
 void withdraw(float);
 void display(void)
 {
 cout<<"Name: "<<p<<endl;
 cout<<"Balance: "<<balance<<endl;
 }
 private:
 float balance,principal;
 char *p,*account_type;
 int account_no;
};
void account::initialize(char *name,int acc_no,char *acc_type,float initial)
{
 int q=strlen(name);
 p=new char[q+1];
 strcpy(p,name);
 account_no=acc_no;
 account_type=acc_type;
 principal=initial;
 balance=initial;
}
void account::deposit(float add)
{
 balance=add+principal;
}
void account::withdraw(float subtract)
{
 balance=principal-subtract;
}
void main()
{
 int i,no;
 char *name,*acc_type;
 float initial;
 account s[2];
 for(i=0;i<2;i++)
 {
  cout<<"Enter name "<<i+1<<": "<<endl;
  cin>>name;
  cout<<"Enter account no :\n";
  cin>>no;
  cout<<"Enter account type: \n";
  cin>>acc_type;
  cout<<"Enter principal amount:\n";
  cin>>initial;
  s[i].initialize(name,no,acc_type,initial);
 }
 for(i=0;i<2;i++)
 {
  s[i].display();
 }
}

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Narue

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Re: Error:Null Pointer assignment

Jan 25th, 2006

>Could you tell me a reason why this is happening?
name and acc_type are uninitialized pointers in main. You're trying to write to memory that you don't own, and the compiler seems to think that's a bad idea. :rolleyes:

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winbatch

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Re: Error:Null Pointer assignment

Jan 25th, 2006

Also, main really should return an int.

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comwizz

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Re: Error:Null Pointer assignment

Jan 26th, 2006

Why should main return an integer ?

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comwizz

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Re: Error:Null Pointer assignment

Jan 26th, 2006

I defined the characters p1 and p2 and initialized the pointers with their address still the program doesnt work and hangs. What should I modify in my program?
Thanks,
comwizz.

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winbatch

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Re: Error:Null Pointer assignment

Jan 26th, 2006

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Originally Posted by comwizz

Why should main return an integer ?

http://www.delorie.com/djgpp/v2faq/faq22_25.html

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Lerner

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Re: Error:Null Pointer assignment

Jan 26th, 2006

The best approach would be to show how you have altered your original code. It should be something like this:

 Help with Code Tags 
 C++ Syntax (Toggle Plain Text) 
int main()
{
   int i,no;
 
   //name and acc_type have no memory associated with them, so you can't use them yet.
   //char *name,*acc_type; 
 
   //allocate some memory to name---say maybe static memory
   char name[80];
 
   //allocate some memory to acc_tpe---try dynamic memory if you wish
   char * acc_type = new char[80];
 
   //now you can put some information in the memory
   cin >> name >> endl;
   cin >> acc_type >> endl;
int main()
{
   int i,no;
   
   //name and acc_type have no memory associated with them, so you can't use them yet.
   //char *name,*acc_type; 

   //allocate some memory to name---say maybe static memory
   char name[80];

   //allocate some memory to acc_tpe---try dynamic memory if you wish
   char * acc_type = new char[80];

   //now you can put some information in the memory
   cin >> name >> endl;
   cin >> acc_type >> endl;

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comwizz

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Re: Error:Null Pointer assignment

Jan 29th, 2006

allocate some memory to acc_tpe---try dynamic memory if you wish.
Without the user specifying the no of letters he is going to enter how should I dynamically allocate memory.for eg. if he is going to enter Dick , I have to allocate 5 bytes without the users specification about the letters he is going to enter i.e. I have to search for a null character and then allocate the memory . I cant figure out how that would be done??
The method you suggested works perfectly fine but would be a wastage of memory as we are taking arrays or allocating memory more than needed.
Thanks,
comwizz.

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comwizz

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Re: Error:Null Pointer assignment

Jan 29th, 2006

Heres my attempt for dynamic memory allocation.

 Help with Code Tags 
 C++ Syntax (Toggle Plain Text) 
//Program to deposit money in a bank account
#include<iostream.h>
#include<string.h>
#include<conio.h>
class account
{
 public:
 void initialize(char *p,int,char *c,float);
 void deposit(float);
 void withdraw(float);
 void display(void)
 {
 cout<<"Name: "<<p<<endl;
 cout<<"Balance: "<<balance<<endl;
 }
 private:
 float balance,principal;
 char *p,*account_type;
 int account_no;
};
void account::initialize(char *name,int acc_no,char *acc_type,float initial)
{
 int q=strlen(name);
 p=new char[q+1];
 strcpy(p,name);
 account_no=acc_no;
 account_type=acc_type;
 principal=initial;
 balance=initial;
}
void account::deposit(float add)
{
 balance=add+principal;
}
void account::withdraw(float subtract)
{
 balance=principal-subtract;
}
void main()
{
 int i,no,count=0;
 char *name,*acc_type,*p;
 float initial;
 account s[2];
 for(i=0;i<2;i++)
 {
  cout<<"Enter name "<<i+1<<": "<<endl;
  cin>>p;
  while(*p!='\0')
  {
   count++;
   p++;
  }
  name=new char[count+1];
  name=p;
  cout<<"Enter account no :\n";
  cin>>no;
  cout<<"Enter account type: \n";
  char *q;
  cin>>q;
  count=0;
  while(*q!='\0')
  {
   count++;
   q++;
  }
  acc_type=new char[count+1];
  acc_type=q;
  cout<<"Enter principal amount:\n";
  cin>>initial;
  s[i].initialize(name,no,acc_type,initial);
 }
 for(i=0;i<2;i++)
 {
  s[i].display();
 }
}
//Program to deposit money in a bank account
#include<iostream.h>
#include<string.h>
#include<conio.h>
class account
{
 public:
 void initialize(char *p,int,char *c,float);
 void deposit(float);
 void withdraw(float);
 void display(void)
 {
 cout<<"Name: "<<p<<endl;
 cout<<"Balance: "<<balance<<endl;
 }
 private:
 float balance,principal;
 char *p,*account_type;
 int account_no;
};
void account::initialize(char *name,int acc_no,char *acc_type,float initial)
{
 int q=strlen(name);
 p=new char[q+1];
 strcpy(p,name);
 account_no=acc_no;
 account_type=acc_type;
 principal=initial;
 balance=initial;
}
void account::deposit(float add)
{
 balance=add+principal;
}
void account::withdraw(float subtract)
{
 balance=principal-subtract;
}
void main()
{
 int i,no,count=0;
 char *name,*acc_type,*p;
 float initial;
 account s[2];
 for(i=0;i<2;i++)
 {
  cout<<"Enter name "<<i+1<<": "<<endl;
  cin>>p;
  while(*p!='\0')
  {
   count++;
   p++;
  }
  name=new char[count+1];
  name=p;
  cout<<"Enter account no :\n";
  cin>>no;
  cout<<"Enter account type: \n";
  char *q;
  cin>>q;
  count=0;
  while(*q!='\0')
  {
   count++;
   q++;
  }
  acc_type=new char[count+1];
  acc_type=q;
  cout<<"Enter principal amount:\n";
  cin>>initial;
  s[i].initialize(name,no,acc_type,initial);
 }
 for(i=0;i<2;i++)
 {
  s[i].display();
 }
}