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C++ Programming for Experienced Engineers

File IO of Numeric and String Data

Explore writing and reading numeric and string data to files in C++. This lesson helps you understand how to use ofstream and ifstream classes for file operations, including opening files, writing data with the insertion operator, reading data back with the extraction operator, and managing file streams effectively.

We'll cover the following...

Challenge

Write a program to write numeric and string data into a file called SAMPLE.TXT. Read the same file back and display the contents read on the screen.

Sample run

root@educative:/usr/local/educative# g++ main.cpp 
root@educative:/usr/local/educative# ./a.out 
Z
25
473.14
Hyperbole!
root@educative:/usr/local/educative# cat SAMPLE.TXT
Z
25
473.14
Hyperbole!

Coding exercise

Your job is to write the code for writing and reading to the file in the main( ) function.

// File IO of numeric and string data
#include <fstream>
#include <iostream>

int main( ) 
{ 		
	char ch = 'Z' ; 	
	int i = 25 ; 	
	float a = 473.14f ; 	
	char str[ ] = "Hyperbole!" ; 
	
	// Your code goes here

	//  send data to screen 	
	std :: cout << ch << std :: endl ;
	std :: cout << i << std :: endl ; 
	std :: cout << a << std :: endl ;
	std :: cout << str << std :: endl ;
	
	return 0 ; 
}

Coding solution

The following code widget has the solution for the challenge explained above.

// File IO of numeric and string data
#include <fstream>
#include <iostream>

int main( ) 
{ 		
	char ch = 'Z' ; 	
	int i = 25 ; 	
	float a = 473.14f ; 	
	char str[ ] = "Hyperbole!" ; 
	
	// create file for output 	
	std :: ofstream outfile ( "SAMPLE.TXT" ) ;  	

	// send data to file 	
	outfile << ch << std :: endl ;
	outfile << i << std :: endl ;
	outfile << a << std :: endl ;
	outfile << str << std :: endl ;
	
	outfile.close( ) ;

	std :: ifstream infile ( "SAMPLE.TXT" ) ;

	//  read data from file 	
	infile >> ch >> i >> a >> str ;

	//  send data to screen 	
	std :: cout << ch << std :: endl ;
	std :: cout << i << std :: endl ; 
	std :: cout << a << std :: endl ; 
	std :: cout << str << std :: endl ;
	
	return 0 ; 
}

Explanation

The contents of the file are displayed on the console using the cat command followed by the filename, like this:

cat SAMPLE.TXT

To begin with, we have defined an object called outfile, of type ofstream ...