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How do I get a C++ program to read input from a text file?

Posted on 2010-11-17
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Last Modified: 2012-05-10
How do I get a C++ program to read input from a text file?  I have a program that works when entering input directly from the console.  I have modified it to accept input from a text file, but it currently will not compile.  It appears that the problem is associated with the paramaters being passed.
#include <iostream>

#include <fstream>  //

#include <strstream>  //

#include <string>

#include <vector>

using namespace std;



#include "DivideByZeroException.h" // DivideByZeroException class

#include "UninitializedException.h" // UninitializedException class

#include "SyntaxException.h" // SyntaxException class



#include "expression.h"

#include "subexpression.h"

#include "symboltable.h"

#include "parse.h"



SymbolTable symbolTable;



void parseAssignments(strstream& in);



int main()

{

	const int SIZE = 256;

	Expression* expression;

    char paren, comma, line[SIZE];

	string variable;  //added for IO file

    double value;     //added for IO file



	ifstream fin("input.txt");

	while (true)

	{

		symbolTable.init(variable, value);

		fin.getline(line, SIZE);

		if (!fin)

			break;

		strstream in(line, SIZE);

		

		in >> paren;

		cout << line << " ";



	//cout << "Enter expression: ";

	//cin >> paren;

 

	try

	{



		if (cin.peek() == '(')  //mistmatch left paren exception.

		{

			throw SyntaxException();

		}



		expression = SubExpression::parse(strstream&);

		

		if (cin.peek() == ')')       //mistmatch right paren exception.

		{

			throw SyntaxException();

		}



		if (cin.peek() != ',')		//missing comma exception. 

		{ 

			throw SyntaxException();

		}



		cin >> comma;

		parseAssignments(in);



		//if (cin.peek() != ';')		//missing comma exception. 

		//{ 

		//	throw SyntaxException();

		//}



		double result = expression->evaluate();

		cout << "Value = " << result << endl;

	}

	catch (DivideByZeroException &divideByZeroException)

	{

		cout << "Error: " << divideByZeroException.what() << endl;

	}

	catch (UninitializedException &uninitializedException)

	{

		cout << "Error: " << uninitializedException.what() << endl;

	}

	catch (SyntaxException &syntaxException)

	{

		cout << "Error: " << syntaxException.what() << endl;

	} 

	}

    return 0;

}



void parseAssignments(strstream& in)

{

    char assignop, delimiter;

    string variable;

    double value;



    do

    {

        variable = parseName();

		in >> ws >> assignop >> value >> delimiter;



		if (assignop != '=')

		{

			throw SyntaxException();

		}

		else

			symbolTable.insert(variable, value);

    }

    while (delimiter == ',');

}

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Question by:NSing9
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7 Comments
 

Author Comment

by:NSing9
ID: 34161155
There appear to be problems with the sysntax here:
#include <iostream>

using namespace std;



#include "SyntaxException.h" // SyntaxException class



#include "expression.h"

#include "subexpression.h"

#include "operand.h"

#include "plus.h"

#include "minus.h"

#include "times.h"

#include "divide.h"



SubExpression::SubExpression(Expression* left, Expression* right)

{

    this->left = left;

    this->right = right;

}



Expression* SubExpression::parse(strstream&)

{

    Expression* left;

    Expression* right;

    char operation, paren;

    

    left = Operand::parse();

    cin >> operation;

    right = Operand::parse();

    cin >> paren;

	switch (operation)

    {

        case '+':

            return new Plus(left, right);

        case '-':

            return new Minus(left, right);

        case '*':

            return new Times(left, right);

        case '/':

            return new Divide(left, right);

		default:

			throw SyntaxException(); 

    }

    return 0;

}

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Author Comment

by:NSing9
ID: 34161162
The definitions are here:
class SubExpression: public Expression

{

public:

    SubExpression(Expression* left, Expression* right);

    static Expression* parse();

protected: 

    Expression* left;

    Expression* right;

};

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Expert Comment

by:trinitrotoluene
ID: 34161565
what is the meaning of this line

Expression* SubExpression::parse(strstream&)

you have to pass an strstream argument else how do you expect the function to do what its supposed to do?

and strstream is deprecated. Consider using stringstream instead.
http://www.cplusplus.com/reference/iostream/stringstream/
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Accepted Solution

by:
trinitrotoluene earned 500 total points
ID: 34161573
this line needs to be corrected

expression = SubExpression::parse(strstream&);

as you can see no argument is being passed
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LVL 12

Expert Comment

by:trinitrotoluene
ID: 34161582
the switch is a bit strange too

switch (operation)
    {
        case '+':
            return new Plus(left, right);
        case '-':
            return new Minus(left, right);
        case '*':
            return new Times(left, right);
        case '/':
            return new Divide(left, right);
            default:


you should be breaking out of a case statement when a specific case matches unless you have a need to do otherwise
0
 

Author Closing Comment

by:NSing9
ID: 34178291
It was understood that the wrong parameters were being assigned.  I had to figure out the correct solution myself.
0
 
LVL 12

Expert Comment

by:trinitrotoluene
ID: 34179691
ofcourse what did you expect? write out the complete solution for you. Thats not what EE does. We are experts not your assistants.
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