Question

Can someone explain the process of this Display a text file program and show the supposed output of the program?

I tried it with my text file and all it does is printing out the same line of words for 24 times. Can you also explain what the [COL_WIDTH + 1 ] and the c = input_line [0] ; is doing?

Please show me what this program is doing. Thanks.

Here below is the actual program.

#include

#include

using namespace std;

#define COL_WIDTH 80

int main() {

int c; // input character

char filename[FILENAME_MAX];

char input_line[COL_WIDTH + 1];

  

cout << "Enter a file name and press ENTER: ";

cin.getline(filename, FILENAME_MAX);

ifstream file_in(filename);

if (! file_in) {

cout << filename << " could not be opened.";

cout << endl;

return -1;

}

while (true) {

for(int i = 1; i <= 24 && !file_in.eof(); ++i) {

file_in.getline(input_line, COL_WIDTH);

cout << input_line << endl;

}

if (file_in.eof()) {

break;

}

  

cout << "More? (Press 'Q' and ENTER to quit)";

cin.getline(input_line, COL_WIDTH);

c = input_line[0];

if (c == 'Q' || c == 'q') {

break;

}

}

return 0;

}

Answer 1

#include<iostream>

#include<fstream>

using namespace std;

#define COL_WIDTH 80

int main() {

int c; // input character

//used to store the file name
//FILENAME_MAX is a predefined constant
//It specify the maximum length for a file name

char filename[FILENAME_MAX];

//used to store the line read from file
//COL_WIDTH is the number of characters to be read from each line
//In COL_WIDTH + 1, 1 is for storing string terminator '\0'
char input_line[COL_WIDTH + 1];

//prompt the user to enter a file name to be read
cout << "Enter a file name and press ENTER: ";

//read the file name and stores in character array 'filename'
cin.getline(filename, FILENAME_MAX);

//make the file to be read
ifstream file_in(filename);

//if file cannot be opened
if (! file_in) {

cout << filename << " could not be opened.";

cout << endl;

return -1;

}

//indefinite while loop
while (true) {

//reads first 24 lines
//file_in.eof() checks whether end of file is reached or not
for(int i = 1; i <= 24 && !file_in.eof(); ++i) {

//reads 79 characters in each line and 80 for '\0'
file_in.getline(input_line, COL_WIDTH);
//display the readed line
cout << input_line << endl;

//if it not reached the end of file
//when the user press enter instead of 'q' or 'Q'
//then above for loop will read from 25th line to next 24 lines
//until reaching end of file

}

//checks whether end of file is reached
//if it is the end , terminate the program
if (file_in.eof()) {
//break the while loop and exit program
break;

}

  
//ask user to continue or quit
cout << "More? (Press 'Q' and ENTER to quit)";
//read the input from user
//and stored to character array 'input_line'
cin.getline(input_line, COL_WIDTH);

// 'c' contains first character in the character array 'input_line'
// 'q' or 'Q'

c = input_line[0];
//if c = 'q' or 'Q'
if (c == 'Q' || c == 'q') {

//terminate while loop and exit program
break;

}

}

return 0;

}

Below file has more than 80 characters in a line, the program read only 79 characters

Output from above text file

If a file cannot be opened