DOC-20241121-WA0004bwushshusjssjuwh..pdf

Using Input / Output Files
A computer file
is stored on a secondary storage device (e.g., disk);
is permanent;
can be used to
provide input data to a program
or receive output data from a program
or both;
should reside in Project directory for easy access;
must be opened before it is used.

General File I/O Steps
1. Include the header file fstream in the program.
2. Declare file stream variables.
3. Associate the file stream variables with the
input/output files by opening the file.
4. Use the file stream variables with >>, <<, or
other input/output functions.
5. Close the file.

Streams
stream - a sequence of characters
interactive (iostream)
•
•
•
• cin - input stream associated with
keyboard.
• cout - output stream associated with
display
file (fstream)
•
•
•
• ifstream - defines new input stream
(normally associated with a file).
•
•
•
• ofstream - defines new output stream
(normally associated with a file).

Stream I/O Library Header Files
Note: There is no “.h” on standard header files : <fstream>
iostream -- contains basic information required for all
stream I/O operations
fstream -- contains information for performing file I/O
operations

File Stream Objects
• There are three types of file stream
objects
(1) ifstream objects: used for input
(2) ofstream objects: used for output
(3) fstream objects: used for both
input and output
13-7

Open() Function
Opening a file associates a file stream variable declared
in the program with a physical file at the source, such
as a disk.
In the case of an input file:
the file must exist before the open statement executes.
If the file does not exist, the open statement fails and the
input stream enters the fail state
An output file does not have to exist before it is
opened;
if the output file does not exist, the computer prepares an
empty file for output.
If the designated output file already exists, by default, the
old contents are erased when the file is opened.

input_stream.open("numbers.txt“)
Open() Function

Important File Functions
getline() - read a line of text from text file store in a string.
Syntax: getline(Input file, String, Delimiting Char);
Example: getline(ifile1, str1, ‘,’);
Example: getline(ifile1, str1);
eof() - This function determines the end-of-file by returning
true(non-zero) for end of file otherwise returning false(zero).
Example : fout.eof( );

Example1: Opening and Closing
#include <fstream>
int main ()
{
ifstream fsIn;//input
ofstream fsOut; // output
//Open the files
fsIn.open("prog1.txt"); //open the input file
fsOut.open("prog2.txt"); //open the output
//Code for data manipulation
//Close files
fsIn.close();
fsOut.close();
return 0;
}

Example2: Writing a string to a file
#include <fstream>
using namespace std;
int main()
{// declare output file variable
ofstream outFile;
// open an exist file fout.txt
outFile.open("fout.txt”);
//behave just like cout, put the word into the file
outFile << "Hello World!";
// Closing the file
outFile.close();
return 0;
}

Example3: Reading from a file -p1
// reading a text file
#include <iostream>
#include <fstream>
#include <string>
int main()
{
string line1;
ifstream myfile;
myfile.open("example.txt");

if (myfile.is_open())
{
while (getline(myfile, line1))
{
cout << line1 << 'n';
}
myfile.close();
}
else cout << "Unable to open file"<< endl;
system("pause");
return 0;
}
Example3: Reading from a file –p2

CSV Files
A Comma Separated Values (CSV) file is a plain
text file that contains a list of data. These files
are often used for exchanging data between
different applications. For example, databases
and contact managers often support CSV files.
These files may sometimes be called Character
Separated Values or Comma Delimited files.
They mostly use the comma character to
separate (or delimit) data.

The Structure of a CSV File
A CSV file has a fairly simple structure. It’s a list
of data separated by commas.
You can open CSV file in Notepad or Excel
Name,Email,Phone Number,Address
Bob Smith,bob@example.com,123-456-7890,123 SF
Mike Jones,mike@example.com,098-765-4321,321 LA

Ex 4: Reading CSV into an Array p1
// reading a text file
// You need to include the below files
#include <iostream>
#include <fstream>
#include <string>
int main()
{
// Define Stage
string line1;
ifstream myfile;
string Info[3][4];
// Opening the file
myfile.open("test1.csv");

{
for (int i = 0; i < 3; i++)
{
for (int j = 0; j < 4; j++)
{
while (getline(myfile, line1,','))
{
cout << line1 << 'n';//show to user
Info[i][j] = line1;//store in Array
}
}
}
myfile.close();
}

system("pause");
return 0;
}

// Writing Array to CSv file
//Include below files
#include <iostream>
#include <fstream>
#include <string>
int main()
{
// Define Stage
int i, j;
ofstream myfile;
string Info[100][4];
Ex 5: Writing Array to CSV file p1

//Input the information from the user
for (int i = 0; i < 100; i++)
{
for (int j = 0; j < 4; j++)
{
cin >> Info[i][j]; // store the user input in the array
}
}
//Output the information to the file
// First open the file
myfile.open("test1.csv");

{
for (int i = 0; i < 100; i++)
{
for (int j = 0; j < 4; j++)
{
myfile << Info[i][j] << ','; // store the data to file
}
myfile << endl; // shift to new line
}
myfile.close();
}
system("pause");
return 0;
}

Ex 6: Passing File Stream Objects to
Functions
//print all integers in a file to screen
void printFile(ifstream &file1)
{
int x;
while(getline(file1,x))
{
cout << x << " ";
}
}
13-24

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