Garbage in char pointer array

Question

terabithia 0 Newbie Poster

14 Years Ago

Hi,
Could someone please let me know how to terminating char pointer array properly?
The menu 0 can successfully generate a set with no garbage value
But other function for ex: Union , Equality
Got a weird character at the back of the array.
ex = S = { A , C, D , H ,L , @}

(Will only find it if we generate a few times)
But i really curious is there any way to not let this happen?

Thank you
SOrry for the bad English
Appreciate your help much!

#include <iostream>
#include <ctime>
#include <cstdlib>
#include <iomanip>
using namespace std;
const int MAX = 10;

typedef char* ptr;
void constructSet (ptr,int);
void printSet (ptr,ptr);
bool checkSet (char ,ptr ,ptr);
void displaySet (ptr,int);
void addInElement (ptr ,ptr&);
void checkElement (ptr , ptr);
int checkCardinality (ptr , ptr);
void Union (ptr first , ptr last);
void Intersection (ptr first,ptr last);
void complement (ptr first,ptr last);
void complementA (ptr,ptr,ptr,ptr,ptr,ptr);
void complementB (ptr,ptr,ptr,ptr,ptr,ptr);
void subset (ptr first,ptr last);
void equality (ptr,ptr);
int checkEqualityS1 (ptr ,ptr ,ptr ,ptr );
int checkEqualityS2 (ptr ,ptr ,ptr ,ptr );
int generateSize ();

int main ()
{
	char a[MAX];
		
	srand( (unsigned int) time(NULL));
	
	int option;
	int size;
	
	do
	{
		cout << "Here are some of the set operations" << endl
			<< endl;
		cout << "0 . An example of set" << endl;
		cout << "1 . Union " << endl;
		cout << "2 . Intersection " << endl;
		cout << "3 . Complement " << endl;
		cout << "4 . Subset of " << endl;
		cout << "5 . Equality " << endl;
		cout << "9 . Quit " << endl 
							<< endl;
		
		cout << "Your choice: ";
		cin >> option;
		cout << endl;
		
		size = generateSize();
		ptr first = &a[0];	  
		ptr last = &a[size-1];	  
			
		switch (option)
		{
			case 0 : displaySet (a ,size);
					 cout << setw(80) << setfill ('-') << " "<<endl;
					break;
			case 1 : Union (first,last);
					 cout << setw(80) << setfill ('-') << " "<<endl;
					break;
			case 2 : Intersection (first,last);
					cout << setw(80) << setfill ('-') << " "<<endl;
					break;
			case 3 : complement (first,last);
					cout << setw(80) << setfill ('-') << " "<<endl;
					break;
			case 4 : subset (first,last);
					cout << setw(80) << setfill ('-') << " "<<endl;
					break;
			case 5 : equality (first,last);
					cout << setw(80) << setfill ('-') << " "<<endl;	 
					break;
		}
		
	}while (option!=9);
	
	return 0;	 	 
}

int generateSize ()
{
	int size;
	size = rand()%MAX+0;
	return size;
}

void displaySet (ptr s,int size)
{
	int option;
		
	ptr first = &s[0];	  
	ptr last = &s[size-1];	  	 
	
	cout << setw(80) << setfill ('-') << " "<<endl;	 
	cout << "Here is an example on set of uppercase letters" << endl << endl;
		
	constructSet (s,size);
	cout << " Set S = " ;
	printSet (first,last);	 
	
	cout << "Note that elements in S are distinct and are not in order " << endl << endl;
	
	int cardinal;
	do
	{
		cout << "Wish to try the following operations?" << endl;
		cout << " 1. Add an element to the set " << endl;
		cout << " 2. Check an element in set " << endl;
		cout << " 3. Check the cardinality" << endl;
		cout << " 9. Quit" << endl 
							<< endl;
		cout << "Your choice : ";
		cin >> option; 
		cout << endl;
	
		switch (option)
		{
			case 1 : addInElement (first,last);
					cout << setw(80) << setfill ('-') << " "<<endl;	 
					break;
			case 2 : checkElement (first,last);
					cout << setw(80) << setfill ('-') << " "<<endl;	 
					break;
			case 3 :cardinal = checkCardinality (first,last);
					cout << "S has " <<  cardinal << " elements " << endl;
					cout << setw(80) << setfill ('-') << " "<<endl;
					break;
			
		}	 
	}while (option!=9);
	
}

void constructSet (ptr s,int size)
{
	ptr ch;
	ptr first = s;
	int i;
	
	for (i = 0;i<=size;i++)
	{
		ch = new char;
		*ch =static_cast <char> ((rand()%26) + 65);
		
		if (checkSet (*ch , first , s)== false)
		{
			*s = *ch;
			++s;
		}
	}
	*s='\0';
}
	
void printSet (ptr first,ptr last)
{

	cout << "{" ;
	
	while (first<last)
	{
		cout << *first << " , " ;
		++first;
	}
	cout << *last<< " } ";	  	   
	cout << endl;
	
}

bool checkSet (char character ,ptr first ,ptr last)
{
	while (first<=last)
	{
		if (character == *first)
			return true;
		else
			first++;
	}
	
	return false;
}

void addInElement (ptr first,ptr& last)
{
	char newElement;
	cout << "Current ";
	printSet (first,last);
	
	cout << "Enter an element : " ;
	cin >> newElement;
	
	if (checkSet (newElement ,first,last)==false)
	{
		last++;
		*last = newElement;
	}
	
	cout << " Set S = " ;
	printSet (first,last);
}
	
void checkElement (ptr first,ptr last)
{
	char character;
	printSet (first, last);
	
	cout <<"Which element?: ";
	cin >> character;
	cout << endl;
	
	if (checkSet ( character, first , last)==false)
	{
		cout << character << " not in" << " S " << endl;
	}
	else
		cout << character << " is in" << " S " << endl;
		
}

int checkCardinality (ptr first, ptr last)
{
	printSet (first,last);
	int sum = 0;
	
	while (first <=last)
	{
		first++;
		sum++;
	}
	
	return sum;
}

//GARBAGE VALUE WHEN IT SUPPOSE TO BE EMPTY SET

void Union (ptr first,ptr last)
{
	ptr first2;
	ptr last2;
	
	int size1 = generateSize();
	int size2 = generateSize();
	
	char a1 [MAX];
	char a2 [MAX];
	
	cout << "Given the following two sets " << endl;
	cout << "Set S1 = ";
		constructSet (a1 , size1);
		
		first = &a1 [0];
		last = &a1 [size1 - 1];
		printSet (first,last);
		
	cout << "Set S2 = ";
		constructSet (a2 , size2);
		
		first2 = &a2 [0];
		last2 = &a2 [size2 - 1];
		printSet (first2,last2);
	
	while (first <= last)
	{
		if (checkSet (*first , first2 , last2)==false)
		{
			last2++;
			*last2 = *first;
			first++;
		}
		else
			first++;
	}
	first++;
		
	cout << " The union is : " ;
	printSet (first2,last2);

}

void Intersection (ptr first,ptr last)
{
	ptr first2;
	ptr last2;
	ptr first3;
	ptr last3;
		

	int size1 = generateSize();
	int size2 = generateSize();
	
	
	char a1 [MAX];
	char a2 [MAX];
	char b [MAX] = { };
	
	cout << "Given the following two sets " << endl;
	cout << "Set S1 = ";
		constructSet (a1 , size1);
		
		first = &a1 [0];
		last = &a1 [size1 - 1];
		printSet (first,last);
		
	cout << "Set S2 = ";
		constructSet (a2 , size2);
		
		first2 = &a2 [0];
		last2 = &a2 [size2 - 1];
		printSet (first2,last2);
	
		first3 = &b[0];
		last3 = &b[0];
							
	while (first <= last)
	{
		if (checkSet (*first , first2 , last2)==true)
		{	 	 	 
			*last3 = *first;	
			last3++;
			first++;	   
		}
		else
		{
			first++;
		}
	}
	last3--;
	
	cout << " The intersection is : " ;	   
	printSet (first3,last3);
}

void complement (ptr first,ptr last)
{
	ptr first2;
	ptr last2;
	ptr first3;
	ptr last3;
	ptr first4;
	ptr last4;
		

	int size1 = generateSize();
	int size2 = generateSize();
	
	
	char a1 [MAX];
	char a2 [MAX];
	char b [MAX] = { };
	char c [MAX] = { };
	
	cout << "Given the following two sets " << endl;
	cout << "Set A = ";
		constructSet (a1 , size1);
		
		first = &a1 [0];
		last = &a1 [size1 - 1];
		printSet (first,last);
		
	cout << "Set B = ";
		constructSet (a2 , size2);
		
		first2 = &a2 [0];
		last2 = &a2 [size2 - 1];
		printSet (first2,last2);
	
		first3 = &b[0];
		last3 =first3;
					
		first4 = &c[0];
		last4 = first4;
	 
	complementA (first,last,first2,last2,first3,last3);
	complementB (first,last,first2,last2,first4,last4);	   

}


void complementA (ptr first,ptr last,ptr first2,ptr last2,ptr first3,ptr last3)
{
		// Complements A-B	  	  
	while (first <= last)
	{
		if (checkSet (*first , first2 , last2)==true)
		{	 	 	 
		   	first++;   
		}
		else
		{
			*last3 = *first;	
			last3++;
			first++;	   	      
		}
	}
	last3--;
	
	cout << endl;
	cout  << "Complements A-B : " ;
	printSet (first3,last3);
}

void complementB (ptr first,ptr last,ptr first2,ptr last2,ptr first4,ptr last4)
{
		//Complements B-A

	while (first2 <= last2)
	{
		if (checkSet (*first2 , first , last)==true) 
		{	 	 	 
			first2++;	         
		}
		else
		{
			*last4 = *first2;	 
			last4++;
			first2++;	    	
		}	 
	}
	last4--;
	
	cout << endl;			
	cout  << "Complements B-A : " ;
	printSet (first4,last4);
}

void subset (ptr first,ptr last)
{
	ptr first2;
	ptr last2;
		

	int size1 = generateSize();
	int size2 = generateSize();
	
	char a1 [MAX];
	char a2 [MAX];
	char b [MAX] = { };
	
	cout << "Given the following two sets " << endl;
	cout << "Set A = ";
		constructSet (a1 , size1);
		
		first = &a1 [0];
		last = &a1 [size1-1];
		printSet (first,last);
		
	cout << "Set B = ";
		constructSet (a2 , size2);
		
		first2 = &a2 [0];
		last2 = &a2 [size2-1];
		printSet (first2,last2);
	
	int sum = 0;
	
	while (first <= last)
		{	 	 	
			if (checkSet (*first , first2 , last2)==true)
			{	
					sum++; 	   	   
					first++;
			}
			else
				first++;	   
		}
	
	
	if (sum == size1)
		cout << " A is subset of B" << endl;
	else
		cout  << "A is not subset of B" << endl;	   	   	   
}


void equality (ptr first,ptr last)
{
	ptr first2;
	ptr last2;
			

	int size1 = generateSize();
	int size2 = generateSize();
	
	
	char a1 [MAX] ;
	char a2 [MAX] ;
	char b [MAX] = { };
	
	cout << "Given the following two sets " << endl;
	cout << "Set A = ";
		constructSet (a1 , size1);
		
		first = &a1 [0];
		last = &a1 [size1 - 1];
		printSet (first,last);
		
	cout << "Set B = ";
		constructSet (a2 , size2);
		
		first2 = &a2 [0];
		last2 = &a2 [size2 - 1];
		printSet (first2,last2);
		
		
	int sizeS1;
	int sizeS2;
	
	if (size1 != size2)
		cout << "It is NOT EQUAL" << endl;
	else 
	{
		sizeS1 = checkEqualityS1 (first,last,first2,last2);
		sizeS2 = checkEqualityS2 (first,last,first2,last2);
		
		if ( (sizeS1 && sizeS2) == true)
			cout << "It is EQUAL" << endl;
		else 
			cout << "It is NOT EQUAL" << endl;
	}
	
}	 

int checkEqualityS1 (ptr first,ptr last,ptr first2,ptr last2)
{
	int sum = 0;
	while (first <= last)
		{
			if (checkSet (*first , first2 , last2)==true)
			{	
					sum++; 	   
					first++;
			}
			else
					return false;	   
		}
	
	return sum;
}

int checkEqualityS2 (ptr first,ptr last,ptr first2,ptr last2)
{
	int sum = 0;
	while (first2 <= last2)
		{
			if (checkSet (*first2 , first , last)==true)
			{	
					sum++;	  
					first2++;
			}
			else
					return false;  
		}
	
	return sum;
}

c++

3 Contributors
3 Replies
149 Views
23 Hours Discussion Span
Latest Post 14 Years Ago Latest Post by dusktreader

Salem 5,199 Posting Sage

14 Years Ago

I would suggest you use std::string for all your strings.
Not raw allocated char pointers.

I can see plenty of places where
- you're not allocating enough memory
- you're not freeing memory you have allocated
- you're not counting the \0 to mark the end of the string
- you're not adding the \0 to mark the end of the string.

Oh, and your typedef saves nothing, and adds confusion.

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terabithia 0 Newbie Poster · Answer 1 · 2010-01-30T22:24:26+00:00

I would suggest you use std::string for all your strings.
Not raw allocated char pointers.
I can see plenty of places where
- you're not allocating enough memory
- you're not freeing memory you have allocated
- you're not counting the \0 to mark the end of the string
- you're not adding the \0 to mark the end of the string.
Oh, and your typedef saves nothing, and adds confusion.

Thanx a lot for the advise
But im actually newbie in pointer.
I don't know how to use the '\0' properly.
In where function i need to add this?

Thanks

dusktreader 137 Posting Whiz in Training · Answer 2 · 2010-01-31T03:32:56+00:00

Hi,
Could someone please let me know how to terminating char pointer array properly?

void constructSet (ptr s,int size)
{
	ptr ch;
	ptr first = s;
	int i;
	
	for (i = 0;i<=size;i++)
	{
		ch = new char;
		*ch =static_cast <char> ((rand()%26) + 65);
		
		if (checkSet (*ch , first , s)== false)
		{
			*s = *ch;
			++s;
		}
	}
	*s='\0';
}

This is probably where the problem you asked about is arising. You're going one step too far on your for loop.

Instead of :
for (i = 0;i<=size;i++)

try
for (i = 0;i<size;i++)

Also, follow the previous suggestions about fixing your memory management.