Trouble with file io

This is a discussion on Trouble with file io within the C++ Programming forums, part of the General Programming Boards category; Hi, I am new to c++ (and programming in general) and have a problem with a small project that I ...

  1. #1
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    Apr 2003
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    2

    Unhappy Trouble with file io

    Hi, I am new to c++ (and programming in general) and have a problem with a small project that I am doing to aid my research. I run multiple Polymerase Chain Reactions to amplify specific sections of DNA from pathogenic bacteria. Anyway, to take some of the pain out of setting these up, I read up a bit and wrote a small c++ programme to calculate the volumes I need for single and multiple PCR reactions. The programme works fine but I would like to add the ability to save the output from my programme to a file. Specifically I would like the programme to invoke the user to name an output file and then for the programme to write to that file and to close the file. I have tried using examples of file io from this site and others but i do not have enough experience or knowledge to implement them properly. I have included the code below. Would anyone be able to point me in the direction of a tutorial that could help me with this, or suggest some additions to my code? The programme was written using emacs on a Mac running mac os 10.2.5 and compiled using g++.

    Thanks in advance

    will

    Code:
    // Mastermix Version 0.4
    // April 2003
    // William Gordon MacKay
    // E-mail - wgmk1d@udcf.gla.ac.uk
    
    #include <iostream.h>
    
    using namespace std;
    
    int main ()
    
    	{
    		cout << endl << endl;
    		cout << "MASTERMIX (version 0.4 [23.04.2003])" << endl << endl;
    		cout << "WG MacKay (wgmk1d@udcf.gla.ac.uk)" << endl << endl;
    		cout << "Please enter the volumes for one PCR (in microlitres) below," << endl << endl;
    		
    		// Defines the PCR reagent variables and prompt the user to asign them values
    		// These PCR reagent variables are then asigned names and printed to the terminal
    
    		int ReturnCode = 0;
    		
    		float pcr = 1;
    		cout << "Total vol:	";
    		cin >> pcr;
    		
    		if (!cin.fail()) // numerical value entered
    		{
    			float pcrB = 1;
    			cout << "Buffer:		";
    			cin >> pcrB;
    		
    		if (!cin.fail()) // numerical value entered
    		{
    			float pcrM = 1;
    			cout << "MgCl2:		";
    			cin >> pcrM;
    		
    		if (!cin.fail()) // numerical value entered
    		{
    			float pcrD = 1;
    			cout << "dNTPs:		";
    			cin >> pcrD;
    		
    		if (!cin.fail()) // numerical value entered
    		{
    			float pcrF = 1;
    			cout << "Forward:	";
    			cin >> pcrF;
    		
    		if (!cin.fail()) // numerical value entered
    		{
    			float pcrR = 1;
    			cout << "Reverse:	";
    			cin >> pcrR;
    		
    		if (!cin.fail()) // numerical value entered
    		{
    			float pcrU = 1;
    			cout << "Undefined:	";
    			cin >> pcrU;
    		
    		if (!cin.fail()) // numerical value entered
    		{
    			float pcrT = 1;
    			cout << "Taq:		";
    			cin >> pcrT;
    									
    		if (!cin.fail()) // numerical value entered
    		{
    			float pcrA = 1;
    			cout << "Target:		";
    			cin >> pcrA;
    		
    		if (!cin.fail()) // numerical value entered
    		{				
    			// The variable water is a special case and is calculated as the "Total volume" - all other volumes
    			float Water = (pcr-(pcrB+pcrM+pcrD+pcrF+pcrR+pcrT+pcrU+pcrA));
    			cout << "Water:	 	" << Water << endl << endl;
    		
    			// Defines the "number of reactions" variable and prompt the use to asign it a value.		
    		
    			float Nr = 1;
    			cout << "Enter number of PCR reactions (+1 to account for pipetting error): ";
    			cin >> Nr;
    			cout << endl;
    			
    				// New variables are defined that are then multiplied by the "number of reactions" 
    				// variable and the corresponding PCR variable.
    				// This produces the PCR reagent variable values for a "PCR mastermix".
    			
    				float Tpcr = Nr*pcr;
    				float TpcrB = Nr*pcrB;
    				float TpcrM = Nr*pcrM;
    				float TpcrD = Nr*pcrD;
    				float TpcrF = Nr*pcrF;
    				float TpcrR = Nr*pcrR;
    				float TpcrT = Nr*pcrT;
    				float TpcrA = Nr*pcrA;
    				float TWater = Nr*Water;
    				
    					// The orginal PCR reagent variables and the new variables (multiplied by the "number of reactions" variable.
    					// This produces a list of PCR reagents and their corresponding volumes (in microlitres) 
    					// for a single PCR reaction and a PCR reaction mastermix
    											
    					cout << endl;
    					cout << "Calculating mastermix..." << endl << endl;
    					cout << "PCR x" << Nr << endl << endl;
    					cout << "Water:		" << TWater << endl;
    					cout << "10X:		" << TpcrB << endl;
    					cout << "MgCl2:		" << TpcrM << endl;
    					cout << "dNTPS:		" << TpcrD << endl;
    					cout << "Forward:	" << TpcrF << endl;
    					cout << "Reverse:	" << TpcrR << endl;
    					cout << "Taq:		" << TpcrT << endl;						
    					cout << "Total Vol:	" << Tpcr << endl;
    					cout << endl << endl;
    		}
    		else
    		{
    			cerr << "ERROR - invalid input" << endl; 
    		
    			cin.clear(); // Clear bad input
    			char BadInput[5]; // Clear up to 5 characters
    			cin >> BadInput;
    		
    			ReturnCode = 1;
    			};
    		}
    		else
    		{
    			cerr << "ERROR - invalid input" << endl;
    			
    			cin.clear(); // Clear bad input
    			char BadInput[5]; // Clear up to 5 characters
    			cin >> BadInput;
    		
    			ReturnCode = 1;
    			};
    		}
    		else
    		{
    			cerr << "ERROR - invalid input" << endl;
    					
    			cin.clear(); // Clear bad input
    			char BadInput[5]; // Clear up to 5 characters
    			cin >> BadInput;
    		
    			ReturnCode = 1;
    			};		
    		}
    		else
    		{
    			cerr << "ERROR - invalid input" << endl;
    		
    			cin.clear(); // Clear bad input
    			char BadInput[5]; // Clear up to 5 characters
    			cin >> BadInput;
    		
    			ReturnCode = 1;
    			};		
    		}
    		else
    		{
    			cerr << "ERROR - invalid input" << endl;
    						
    			cin.clear(); // Clear bad input
    			char BadInput[5]; // Clear up to 5 characters
    			cin >> BadInput;
    
    			ReturnCode = 1;
    			};		
    		}
    		else
    		{
    			cerr << "ERROR - invalid input" << endl;
    		
    			cin.clear(); // Clear bad input
    			char BadInput[5]; // Clear up to 5 characters
    			cin >> BadInput;
    		
    			ReturnCode = 1;
    			};
    		}
    		else
    		{
    			cerr << "ERROR - invalid input" << endl;
    		
    			cin.clear(); // Clear bad input
    			char BadInput[5]; // Clear up to 5 characters
    			cin >> BadInput;
    	
    			ReturnCode = 1;
    			};
    		}
    		else
    		{
    			cerr << "ERROR - invalid input" << endl;
    		
    			cin.clear(); // Clear bad input
    			char BadInput[5]; // Clear up to 5 characters
    			cin >> BadInput;
    	
    			ReturnCode = 1;
    			};
    		}
    		else
    		{
    			cerr << "ERROR - invalid input" << endl;	
    		
    			cin.clear(); // Clear bad input
    			char BadInput[5]; // Clear up to 5 characters
    			cin >> BadInput;
    		
    			ReturnCode = 1;
    		};
    		
    	cout << "Goodluck" << endl << endl;
    	
    	return 0;
    }

  2. #2
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    Join Date
    Apr 2003
    Posts
    2,662
    Code:
    #include <fstream>//for fstream objects
    #include <iostream>
    
    using namespace std;
    
    int main()
    {
    	char filename[50];
    	cout<<"Enter a file name for output "
    	    <<"(e.g. C:\\MyFolder\\my_file.text):"<<endl;
    
    	cin.getline(filename, 50);
    
    
    	fstream output_file(filename);
           //associates the file with an fstream object and opens the file
    	int calculation=4*50 + 2;
    	output_file<<calculation;
    
    	output_file.close();
    
    	return 0;
    }
    Example of execution:

    Enter a file name for output (e.g. C:\MyFolder\my_file.text):
    C:\TestData\output.txt
    Press any key to continue

    output.txt
    ----------
    202


    P.S. Do you think this was in any way helpful in explaining that you don't know how to do file I/O:

    I run multiple Polymerase Chain Reactions to amplify specific sections of DNA from pathogenic bacteria
    Last edited by 7stud; 04-25-2003 at 07:11 PM.

  3. #3
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    Apr 2003
    Posts
    2
    7stud said,

    "P.S. Do you think this was in any way helpful in explaining that you don't know how to do file I/O:

    I run multiple Polymerase Chain Reactions to amplify specific sections of DNA from pathogenic bacteria"

    I thought I was being polite by puting the code in context. Apologies.

    Thanks for the advice

    will

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