I am trying to read the first line of a file.
cout << "File: " << endl;
string fileName;
cin >> fileName;
cout << fileName << endl;
ifstream infile(fileName);
string line;
getline(infile,line,'\n');
cout << line << endl;
I am using CodeBlocks and I have a file named "1.txt" in the same directory as main.cpp.
This file contains 2 lines of thext, but the line variable is always empty. What am I missing here?
So after a LOT of searching I finally realized that I used notepad instead of notepad++ and the file got named as 1.txt.txt
Leaving this answer if anyone has the same problem in the future.
Related
I'm trying to open a C++ .txt file as shown in my code below. This is part of a larger program that I'm working on where I write the contents of one file into another so that it contains the same information as the original but I am required to provide user-input. If the user-provides a .txt file that is not the one we are using, I have to produce an error message and prompt them to re-enter an input until they input the correct one (test.txt):
#include <iostream>
#include <fstream>
#include <string>
using namespace std;
int main()
{
/* Refers to test.txt */
ofstream mainfile;
std::string filename;
std::cout << "Please enter the name of your data file: ";
std::cin >> filename;
mainfile.open(filename.c_str());
mainfile << "test.txt";
if(!mainfile) {
std::cout << "I'm sorry, I could not open '" << filename << "'." << std::endl;
std::cout << "Please enter another name: " <<
std::endl;
std::cin >> filename;
} else {
std::cout << "File '" << filename << "' opened successfully!" << std::endl;
}
return 0;
}
My current issue is that the program is terminating too early, even when I input incorrect inputs such as jaguar.txt or flowers.txt, anything that isn't "test.txt". In fact, when I input just about any .txt file name it will output saying that it opened successfully.
It seems that what you want to do is open up 2 different files, where one is used as the file to copy from (test.txt), and the other is the file to copy to (jaguar.txt). Instead of checking if test.txt exists with std::ofstream, you should instead use std::ifstream.
Using ifstream, if the file does not exist, your code will work properly. Instead, because you are currently using ofstream, the file will open correctly, because you're essentially telling it to make the file for you.
So basically, where you have used ofstream mainfile, instead it should be:
ifstream mainfile;
Later in the code, you can prompt the user for the file to copy to (i.e. jaguar.txt), and this will be the one where you output data using ofstream.
Use ifstream to read from a file, and ofstream to write to a file.
To check whether the source file exists, test the corresponding ifstream after trying to open it:
ifstream mainfile; // ifstream stands for "input file stream"
std::cout << "Please enter the name of your data file: ";
std::cin >> filename;
mainfile.open(filename);
while (!mainfile) { // asking endlessly, until the user inputs a good file
std::cout << "I'm sorry, I could not open '" << filename << "'." << std::endl;
std::cout << "Please enter another name: " <<
std::endl;
std::cin >> filename;
mainfile.open(filename);
}
std::cout << "File '" << filename << "' opened successfully!" << std::endl;
By the way, in the error message "open" is programmer's jargon. It's a general word which includes both reading and writing. If your application copies stuff from one file to the other, the user may get confused: is there a problem with input or output? You might want to say "read" instead of "open", even though technically you didn't read anything yet. That would make a clearer error message.
If you want to copy one file to another, use one of the methods described in a dedicated question.
This is my code here.
ifstream inFile;
ofstream outFile;
string line, line2;
inFile.open("DATA.txt");
outFile.open("DATA.txt");
getline(inFile, line);
cout << line;
getline(inFile, line2);
cout << line2;
getline(cin, line);
getline(cin, line2);
outFile << line << "\n" << line2;
From what I understand, getline(inFile, line) should assign the first line of my text file to a string named line. Then the cout << line should print that string into the cmd window. This is not working though.
I am able to input just fine using getline(cin, line) and outFile though. The file gets updated and I can see what I typed in it, but it just doesn't properly read and print the lines.
p.s This is my first question and I'm not entirely sure how to ask it in the title so I'm open to criticism.
On most platforms, std::cout typically buffers output data and does not flush to the console until a line break is output, or the buffer is flushed explicitly.
Try using:
cout << line << '\n';
Or:
cout << line << endl;
If you don't want to output line breaks, use:
cout << line << flush;
So I figured it out. When I had
inFile.open("DATA.txt");
outFile.open("DATA.txt");
I think the outFile.open overwrote the inFile.open, causing only the output part to work.
Simply moving the outFile.open to before the output part instead of before everything fixed this problem. I'm sure there are several other sloppy things about my code, but that fixed it to the point of actually working.
Note: I am using the C++11 standard, so I don't see why this isn't working with or without c_str() appended.
I have the following code:
// open streams
ifstream in(input);
ofstream out(output);
// get which file to open
in.ignore(INT_MAX, ':'); // we don't need the beginning part
in.ignore(); // remove trailing whitespace
string fileLocation;
getline(in, fileLocation);
out << "Loading: " << fileLocation << endl;
cout << "Loading: " << fileLocation << endl;
// now that we know where the file is, load it:
ifstream file(fileLocation);
which reads from a file that looks vaguely like this
File: file.txt
(Subcommands below)
I know that I am pulling the correct filename because of the terminal output.
Anyway, I noticed that the stream wasn't opening properly, so I added this conditional to check:
if ( !file )
{
cout << "File wasn't loaded properly." << endl;
}
And sure enough, I see that message when running the program.
My question is this: how come, when I hard-code the file location, e.g. ifstream file("file.txt") it opens up no problem? How do I get this working properly?
What I would like the user to do is type a file name in such as testquote and then for my program to add .txt to the end to save the file as a .txt, this is so I can save multiple quotes to the computer without over writing. This is what I have so far:
cout << "What would you like to save the quotation as? (Maybe using your last name) " << endl;
cin >> nameOfFile;
ofstream outfile; // Opens file in write mode
outfile.open(nameOfFile)<<(".txt"); // Opens the quotations file
//Lawn
outfile << "The total lawn area is " << lawnArea << " square meters" << endl; // Writes users data into the file
outfile << "The total cost for the lawn is £" << (lawnArea * lawnCost) << endl; // Writes users data into the file
Assuming nameOfFile is a std::string, you can use std::string::operator+ to concatenate it with ".txt":
ofstream outfile(nameOfFile + ".txt");
(Note: there's no need to call open - just pass the filename to the constructor)
outfile.open(nameOfFile)<<(".txt"); // Opens the quotations file
This line of code is simply wrong. You seem to be confused with usage of the operator<< in conjunction with the std::ofstream class.
What you want is a std::string variable containing the name of the file to be opened. Appending a .txt extension should be done automatically, right?
So first have a variable to receive the users file name choice (without the .txt):
std::string nameOfFile;
// ...
cin >> nameOfFile;
Then append a .txt:
nameOfFile += ".txt";
Then construct a std::ofstream with this string:
std::ofstream outfile(nameOfFile.c_str());
After the program reads the file, gets characters from the file, and finishes, the user is asked if they want another file read or not. If the user say yes, then the program asks for the file name, but then automatically says the file could not be opened and exits the loop. Please help me.
Here is the code:
do //do while opening the source file fails
{
cout << "Enter filename of source file: ";
cin.getline (filename,51);
sourceFile.open(filename); //opens the file with given filename
if (sourceFile.fail())
cout << "File could not be opened" << endl; //error if can't open
sourceFile.clear();
}
while (sourceFile.fail()); //exits if source file doesn't fail
This test:
while (sourceFile.fail())
will never be true because just before you get there you call:
sourceFile.clear()
which will clear any problem bits in the iostate for the stream.
I think you just want to get rid of the call to clear().
The canonical way to check if opening the file failed is to use std::basic_ios::operator !():
do
{
cout << "Enter filename of source file: ";
std::getline(std::cin, filename);
sourceFile.open(filename.c_str());
if (!sourceFile)
{
cout << "File could not be opened" << endl;
}
}
while (!sourceFile);