This code should give you a simple recipe type of instruction to learn how to handle file input and output operations. The biggest challenge is to understand your file system navigation with Windows Explorer and the location of your source files.
Create an input file with a simple editor like Notepad.exe and make sure you know where you save the input file to. Do not use spaces in creating the input file name. also, understand the input file name does not have to match the ifstream variable name. You can name your input file anything you'd like, just type the same file name when you open the file in your code.
In this example, the
input_file.txt content is
92A98.76.
Start with a skeleton program like this one and place your pseudo code into the skeleton program as comments.
Write pseudo code
1. Include strings in case if we need to specify a string for a file name
2. This library is needed for handling file input and output, ifstream, ofstream
Declare variables to store data read from file
3. Declare input file variable
4. Declare output file variable
4.1 Make sure there is an input file with proper data ( read only ) and your userID has write access to output location
5. Open input and output files. The input file should be placed on the
same path with your source code. The output file will be written into
the same path as your source code.
if you need to specify a path to the file, escape the backslash
6. Use filestream variables like we use iostream variables
7. Close input and output files
Create actual skeleton program with pseudo code copied in as comments
#include <iostream>
//cin, cout, endl
//1. include strings in case if we need to specify a string for a file name
//2. this library is needed for handling file input and output, ifstream, ofstream
using namespace std;
int main()
{
//Declare variables to store data read from file
//3. declare input file variable
//4. declare output file variable
//4.1 make sure there is an input file with proper data ( read only ) and your userID has write access to output location
//5. open input and output files. The input file should be placed on the same path with your source code. The output file will be written into the same path as your source code.
//if you need to specify a path to the file, escape the backslash
//6. use filestream variables like we use iostream variables
//cin >> x >> grade >> y;
/* cout << "Your test score is: " << x << endl;
cout << "Your letter grade is: " << grade << endl;
cout << "Your class average is" << y << endl; */
//7. close input and output files
return 0;
}
Complete the code by first writing the cin/cout way of reading and printing values and change that to ifstream and ofstream variables later.
#include <iostream>
//cin, cout, endl
#include <string>
//1. include strings in case if we need to specify a string for a file name
#include <fstream>
//2. this library is needed for handling file input and output
// ifstream, ofstream
using namespace std;
int main()
{
//Declare variables to store data read from file
char grade;
int x;
float y;
//3. declare input file variable
ifstream inFile;
//4. declare output file variable
ofstream outFile;
//4.1 make sure there is an input file with proper data ( read only ) and your userID has write access to
// output location
//5. open input and output files
inFile.open("c:\\dell\\input_file.txt");
//if you need to specify a path to the file, escape the backslash
outFile.open("c:\\temp\\output.txt");
//6. use filestream variables like we use iostream variables
//cin >> x >> grade >> y;
inFile >> x >> grade >> y;
/* cout << "Your test score is: " << x << endl;
cout << "Your letter grade is: " << grade << endl;
cout << "Your class average is" << y << endl; */
outFile << "Your test score is: " << x << endl;
outFile << "Your letter grade is: " << grade << endl;
outFile << "Your class average is" << y << endl;
//7. close input and output files
inFile.close();
outFile.close();
return 0;
}
Compile the code by placing break points before and after the read operations. Read the values for the variables before and after the read operations to identify problems with your input file.
Note: Later on, we'll learn how to validate input and code proper exit if the input or output files can not be manipulated.
if(!inFile){
//validate input
cout<<"Input file can not be located!"<<endl;
return 2;
//return a value to indicate error condition
}
if(!outFile){
//validate output
cout<<"You do not have enough space to store the output or you do not have right to write output at this location!"<<endl;
return 4;
//return a different value to indicate error condition
}
Read file into a c_string one line at a time.
ifstream inFile;
inFile.open("input.txt");
const int SIZE = 30;
if (!inFile){
cout << "Input file was not found.";
return 2;
}
char lineRead[SIZE];
while (!inFile.eof()){ //check to see if the end of the file is reached
inFile.getline(lineRead, SIZE-1, '\n');
cout << lineRead << endl;
}
inFile.close();
Read lines in a loop and make sure the first line is not empty before entering the loop.
ifstream inFile;
inFile.open("input.txt");
const int SIZE = 30;
if (!inFile){
std::cout << "Input file was not found.";
return 2;
}
char lineRead[SIZE];
inFile.getline(lineRead, SIZE - 1, '\n');
while (!inFile.eof() && lineRead[0]!='\0'){ //
std::cout << lineRead << endl;
//for (char ch : lineRead) cout << ch << endl; //if you want to see each character read
inFile.getline(lineRead, SIZE - 1, '\n');
}
inFile.close();
