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Calling an object within a class

DyslexicChciken (92)
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class abc {

	public:

	int i;
	abc * foooo;

};


How do you call * foooo? Say I create:

abc a;

* foooo would have some values for int i.

To get int i of *foooo, I tried a.foooo.i, which doesn't work. How do you call it?
Last edited on
Daleth (1030)
To access a class member through a pointer, you need to use the -> operator.
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abc a, b;

a.foooo = &b;

a.foooo->i = 77; //Same as writing b.i = 77;
ne555 (10692)
foooo is a pointer, so a.foooo->i
make sure that it does point to a valid location.
DyslexicChciken (92)
In the code below(I omitted the stuff that I don't think will be important) row_str and col_str are strings input by the user.
a[i][j] is a two dimensional dynamic array of type 'abc'.

Here is a more descriptive class:

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class abc {

	public:

	int i;
	int j;
	abc * back;

};

int d(string &s, string &t, int i, int j)
{
	if(s[i]==t[j])
	{
		return 0;

	}

	else  

		return 1;

}

int min(int a, int b, int c)

{
	int x[3]={a,b,c};
	int y=a;

	for(int i=1; i<3; i++)
	{
		if(x[i]<y)

			y=x[i];

	}

	return y;

}


In the main function, I am getting segmentation fault error on anything that uses arrows '->'. My teacher hasn't taught how to use arrows yet, so I don't really know how to use it properly.


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for(int r=1; r<row_str.length(); r++)

	{



		for(int c=1; c<col_str.length(); c++)

		{

			a[r][c].value=min(a[r-1][c-1].value+d(row_str,col_str,r,c), a[r-1][c].value+1, a[r][c-1].value+1);

			if(a[r][c].value==a[r-1][c-1].value+d(row_str,col_str,r,c))
			{
//segmentation fault errors in lines with arrows.
//Basically I want a[r][c].back->i to equal the last row r-1.
//And I want a[r][c].back->j to equal the last column c-1.
				a[r][c].back->i= r-1;
				a[r][c].back->j= c-1;

			}

			else if(a[r][c].value==a[r-1][c].value+1)
			{
				a[r][c].back->i= r-1;
				a[r][c].back->j= c;

			}
			else if(a[r][c].value==a[r][c-1].value+1)

			{
				a[r][c].back->i= r;
				a[r][c].back->j= c-1;

			}

		}


	}



Full code is below:

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#include <iostream>
#include <string>
using namespace std;

class Entry {

	public:

	int i;
	int j;
	int value;
	//Entry *back can be set as an array.
	Entry * back;

};

int d(string &s, string &t, int i, int j)
{
	if(s[i]==t[j])
	{

		return 0;

	}

	else  

		return 1;

}



int min(int a, int b, int c)
{


	int x[3]={a,b,c};

	int y=a;

	for(int i=1; i<3; i++)
	{

		if(x[i]<y)

			y=x[i];

	}

	return y;

}



int main()
{

	string row_str="_", col_str="_";

	string row_in, col_in;



 	cout<<"This program outputs the edit distance of two strings.\n"

			<<"Enter the first string.\n";

	cin>>row_in;

	cout<<"Enter the second string.\n";

	cin>>col_in;

	row_str=row_str+row_in;

	col_str=col_str+col_in;

	Entry**a=new Entry*[row_str.length()];

	for(int i=0; i<row_str.length(); i++)
	{

		a[i]=new Entry[col_str.length()];

	}


	for(int x=0; x<row_str.length(); x++)
	{

		a[x][0].value=x;
		a[x][0].i=0;
		a[x][0].j=x;


		//cout<<"a[x][0].i: " << a[x][0].i << "x: " << x << ".\n";

	}


	for(int y=0; y<col_str.length(); y++)

	{

		a[0][y].value=y;
		a[0][y].i=y;
		a[0][y].j=0;

		//cout<<"a[0][y].j: " << a[0][y].j << "y: " << y << ".\n";

	}



/*
	for(int r=0; r<row_str.length(); r++)

	{

		for(int c=0; c<col_str.length(); c++)
		{

				cout<<a[r][c].value<<' ';

		}

		cout<<"\n";

	}
*/

	int e_size=0;
	
	if(	col_str.length()>=row_str.length() )
		e_size=col_str.length();

	else if( col_str.length()<=row_str.length() )
		e_size=row_str.length();

	//a[0][0].back=new Entry[e_size];


	for(int r=1; r<row_str.length(); r++)
	{

		for(int c=1; c<col_str.length(); c++)
		{
			a[r][c].value=min(a[r-1][c-1].value+d(row_str,col_str,r,c), a[r-1][c].value+1, a[r][c-1].value+1);
			cout<< "r: " << r << "c: " << c << "\n";
			cout<<"a[r][c].value: " << a[r][c].value << "\n";
			cout<<"a[r-1][c-1].value+d(row_str,col_str,r,c): " << a[r-1][c-1].value+d(row_str,col_str,r,c) << "\n";	
			cout<<"a[r-1][c].value+1: " << a[r-1][c].value+1 << "\n";	
			cout<<"a[r][c-1].value+1: " << a[r][c-1].value+1 << "\n";	
			cout<<"a[r][c].back: " << a[r][c].back << "\n";	
			cout<<"a[r][c].back->i: " << a[r][c].back->i << "\n";
	

			if(a[r][c].value==a[r-1][c-1].value+d(row_str,col_str,r,c))
			{
			//This assigns to *a[r][c].back the value a[r-1][c-1], because a[r][c] is jumped from a[r-1][c-1].


				a[r][c].back->i= &a[r-1][c-1];
				//a[r][c].back->j= x.j;

				cout<<"a[r][c].back->i: " << a[r][c].back->i << "\n";

			}

			else if(a[r][c].value==a[r-1][c].value+1)
			{
				a[r][c].back->i= r-1;
				a[r][c].back->j= c;

			}
			else if(a[r][c].value==a[r][c-1].value+1)

			{
				a[r][c].back->i= r;
				a[r][c].back->j= c-1;

			}

		}

	}


	cout<<"The rows represent the first string you entered plus a beginning space character: \n"

			<<row_str<<"\n"

		  <<"The columns represent the second string you entered plus a beginning space character: \n"

			<<col_str<<"\n";

	cout<<"\n";

	cout<<"\n\nThe editing distance is:\n"
	  <<a[row_str.length()-1][col_str.length()-1].value;
Last edited on
requiem31 (13)
In the main function, I am getting segmentation fault error on anything that uses arrows '->'. My teacher hasn't taught how to use arrows yet, so I don't really know how to use it properly.


I will do you a big favor. http://lmgtfy.com/?q=c%2B%2B+arrow+operator
TwilightSpectre (1392)
Look at it this way - a->b is the same as (*a).b.

Now, in your program, you are dereferencing back. However, you never set back to point to anything, and then you are setting 'i' to the address of something else; but in the process of doing this you dereference back (which isn't pointing anywhere sensible yet). You may want to reconsider lines 148 to 188.
Last edited on
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