File Input/Output

External Files

• Batch– Requires use of data files (save to disk)– Batch can be run during off peak use– allows things to be complete at start of day

• Interactive– Real time systems– Ok for smaller programs– Programs that complete quickly

Files

• Naming– .cpp .dat .out .in .txt

• How to attach files to the stream– stream object– external file name– internal name– open– close

• Additional functions as part of <fstream> class

Files

•Declare the stream to be processed need to #include <fstream>ifstreamins; // ins is the internal file name for input modeofstream outs; // outs is the internal file name for output mode

•Need to open and close the filesins.open (“input.txt”); //”input.txt” and “output.out” are eternal file namesouts.open (“output.out”);ins >> number;outs << number;ins.close();outs.close ();

Creating a Sequential File

• Open the file. Specify: – External name: the full name of the file on disk.– Internal name: the name by which the file will be

known in the program.– File mode: the purpose of the file: input or output.

• Write data to the file, or read data from, the file.• Close the file.

– Saves the file and puts an end-of-file marker after the last record if the file was created in the program.

– Closes the file if the file is an input file.

Example

• If we issue the command ‘Open ‘GRADES” for Output As NewFile’– GRADES is the external name– NewFile is the internal name– The mode is output

• If we issue the command ‘Close NewFile’– Puts the EOF marker.– Closes the file.– Saves the file with the external name ‘GRADES.’

Reading a File

• To open: ‘Open “GRADES “ for Input As GradeFile’• Read the internal filename and the fields/variables

– Read GradeFile, Name, Score• Read records within a loop.

While Not EOF(GradeFile)

Read GradeFile, Name,Score

….

End While

Close GradeFile

// fileapp.cpp#include <iostream>#include <fstream> // necessary for file I/O#include <string> // necessary for string objectusing namespace std;

int main(){

string user_name;int age; ofstream outfile; // Declare file stream named outfile.

cout << "Enter your name: "; // Get name from user.getline(cin, user_name);cout << "Enter your age: "; // Get age from user.cin >> age;

outfile.open("NAME_AGE.TXT",ios::out); // Open file for output.

if (outfile) // If no error occurs while opening file/ write the data to the file.{ outfile << user_name << endl; // Write the name to the file.

outfile << age << endl; // Write the age to the file.outfile.close(); // Close the output file.

}else // If error occurred, display message.{

cout << "An error occurred while opening the file.\n";}return 0;

}

// numread.cpp#include <fstream> #include <iostream>#include <iomanip>using namespace std;

int main(){ float x, sum;

int count;ifstream infile; // Declare file stream named infile.infile.open("FLOATS.TXT",ios::in); // Open file for input.

sum = 0.0; count = 0; if (infile) // If no error occurred while opening file input the data from the file{

cout.setf(ios::fixed); cout << "The numbers in the data file are as follows:\n"<< setprecision(1);

do // Read numbers until 0.0 is encountered.{

infile >> x; // Get number from file.cout << x << endl; // Print number to screen.sum = sum + x; // Add number to sum.count++; // Increment count of how many numbers read.

} while(x != 0.0);

// Output sum and average.cout << "The sum of the numbers is " << sum << endl;cout << "The average of the numbers (excluding zero) is " << sum / (count - 1) << endl;

}else // If error occurred, display message.{

cout << "An error occurred while opening the file.\n";}infile.close(); // Close the output file.return 0;

}

// num_end.cpp#include <fstream> #include <iostream>#include <iomanip>using namespace std;int main(){ double x, sum;

int count;ifstream infile; // Declare file stream named infile.infile.open("NUMS.TXT",ios::in); // Open file for input.sum = 0.0; count = 0; if (infile) // If no error occurred while opening file input the data from the file{. cout.setf(ios::fixed); cout << "The numbers in the data file are as follows:\n"<< setprecision(1);

do // Read numbers until the end of file is encountered.{infile >> x; // Get number from file.if(!infile.fail()) // If the end of file is not reached...{ cout << x << endl; // Print number to screen. sum = sum + x; // Add number to sum. count++; // Increment count of how many numbers read.}} while(!infile.fail());// Output sum and average.cout << "The sum of the numbers is " << sum << endl;cout << "The average of the numbers is " << sum / count << endl;}else // If error occurred, display message.{cout << "An error occurred while opening the file.\n";}infile.close(); // Close the output file.return 0;

}

// num_end.cpp#include <fstream> #include <iostream>#include <iomanip>using namespace std;int main(){ double x, sum;

int count;ifstream infile; // Declare file stream named infile.infile.open("NUMS.TXT",ios::in); // Open file for input.sum = 0.0; count = 0; if (infile) // If no error occurred while opening file input the data from the file{. cout.setf(ios::fixed);

cout << "The numbers in the data file are as follows:\n"<< setprecision(1);

infile >> x; // Get number from filewhile ( !infile.fail() ){ cout << x << endl; // Print number to screen. sum = sum + x; // Add number to sum. count++; // Increment count of how many numbers read. infile >> x; // Get number from file.}// Output sum and average.cout << "The sum of the numbers is " << sum << endl;cout << "The average of the numbers is " << sum / count << endl;

}else // If error occurred, display message.{

cout << "An error occurred while opening the file.\n";}infile.close(); // Close the output file.return 0;

}

Pseudocode Language (Ch 5)

In this chapter we added specific data type declarations, some numeric functionsand file I/O

Declarations: Functions:Int(Variable)

Declare Variable As Data Type Random(Variable)Sqrt(Variable)

File I/O:

Open “file” For Input/Output As NameClose Name

Read Name, VariableWrite Name, Variable

EOF(Name)