I'm working on my first file handling in C++. I have written a simple program, but the problem is ofstream is now working in Dev C++. Any suggests?
#include<iostream>
#include<fstream>
#include<string>
using namespace std;
int main(){
ofstream file_;
file_.open("mytext.txt");
file_ << "This is my first text file ";
file.close();
std::cin.get();
return 0;
}
As mindriot said in his comment, this is a compile error, use instead:
file_.close ();
Related
Basically, I'm following a simple tutorial about files handling in C++.
I've been trying to create and write into a txt file at the same time, but any of the methods I've tried won't actually create a txt file in my executable location.
I should also say that, I print myfile.is_open() just to know if the file truly created and opened, but I get 0 everytime with every method.
What am I doing wrong ?
I mainly tried to create and write to a txt file like this:
#include <iostream>
#include <fstream>
using namespace std;
int main()
{
fstream myfile;
myfile.open("example.txt", ios::out);
cout << myfile.is_open() << endl;
myfile << "Writing this to a file.\n";
myfile.close();
}
First, I bet you're using an IDE like Visual Studio. Most IDEs set your working directory somewhere other than your project directory. I don't use Visual Studio, but many of them put them in ../.
So your file is being produced, but not where you think you should find it.
If you compile and run this program without an IDE, you'll get your file where you expect it.
You may also be able to tell your IDE that the working directory should be your project directory.
Now, to keep you from making a few bad habits, I'm going to tell you two more things.
It's considered a mistake to do using namespace std. Instead, I do using statements only on those things I am going to use frequently. In your short code, I wouldn't have done any.
Next, if you're going to write out a file, it's better to use std::ofstream. It's otherwise the same code. But it's a bit clearer that you're only using the file for output.
So my version of your code:
#include <iostream>
#include <fstream>
int main()
{
std::ofstream myfile;
myfile.open("example.txt");
std::cout << myfile.is_open() << std::endl;
myfile << "Writing this to a file.\n";
myfile.close();
}
Yeah, those std:: everywhere can be annoying, so you could do this:
#include <iostream>
#include <fstream>
using std::ofstream;
using std::cout;
using std::endl;
int main()
{
ofstream myfile;
myfile.open("example.txt");
cout << myfile.is_open() << endl;
myfile << "Writing this to a file.\n";
myfile.close();
}
I actually have an include of CommonUsing.h that I put a few things I do almost everywhere.
#pragma once
#include <chrono>
#include <iostream>
#include <date/date.h>
//======================================================================
// The most common using statements I do in most of my code.
//======================================================================
using std::cout;
using std::cerr;
using std::endl;
using std::string;
using namespace std::chrono_literals;
using date::operator<<;
I just installed mingw on my Windows 10 computer and wanted to code a program that read two files. I immediately faced a frustrating bug with ifstream: when I declare more than one ifstream, the program seems to crash (nothing is logged although the first line cout some text).
The following code compiles and logs "test" in the console:
#include <iostream>
#include <fstream>
using namespace std;
int main()
{
cout << "test" << endl;
ifstream test;
return 0;
}
The following code compiles but seems to crash at runtime, nothing is logged:
#include <iostream>
#include <fstream>
using namespace std;
int main()
{
cout << "test" << endl;
ifstream test;
ifstream test2;
return 0;
}
I tested the exact same codes on a macOS Mojave and both codes work and log "test".
I guess the issue is related to the g++ installation but I'd like to know what's really happening and how I can fix this on Windows.
In my code below errors occur and the program will not run, I am required to make a Constructor that must open the file with the given filename. If the filename does not exist then it Prints an error message and terminates the program.
Below is the code that I have done so far in C++:
#include "ReadWords.h"
#include <iostream>
#include <cstdlib>
using namespace std;
ReadWords::ReadWords(const char filename[])
{
wordfile.open(filename);
if (!wordfile)
{
cout << "cannot make " << filename << endl;
exit(1);
}
}
void ReadWords::close()
{
wordfile.close();
}
Why dont you try including fstream to the top of your file and see if that works
I suppose wordfile is of type std::fstream. If your ReadWords.h #includes <fstream>, it should work (compiles and works as expected).
By the way, it's a bad practice to use using namespace std;.
Also, since you use C++, take a look at std::string. It's safer than using plain char* or char[].
I have a program showing error. How to resolve the error and to use ostream to display output
I use g++ compiler in my ubuntu
#include<iostream>
using namespace std;
int main()
{
ostream out;
out<<"Hello World";
}
The ostream that you want (attached to the display) has already been defined as cout.
#include<iostream>
using namespace std;
int main()
{
cout<<"Hello World";
}
Not all ostreams send the stream to the terminal display.
std::ostream does not have a default constructor, this:
ostream out;
will be a compile time error.
You are probably wanting to use std::cout (as has already been stated).
Firstly, include #include <fstream> . Secondly, change ofstream out to ofstream out("file.txt") .
#include <iostream>
#include <fstream>
using namespace std;
int main () {
ofstream out ("c:\\test5.txt");
out<<"Hello World";
out.close();
return 0;
}
In order to do some output you need to get the right ostream. As Drew Dormann showed you, you can use std::cout for writing on standard output. You can also use std::cerr for the standard error, and finally you can instantiate your own fstream if you want, for instance, to write on a file.
#include <iostream>
#include <fstream>
int main()
{
std::fstream outfile ("output.txt", fstream::out);
outfile << "Hello World" << std::endl;
// Always close streams
outfile.close();
}
As side note: i suggest not to export the std namespace (use namespace std) in your programs (see this faq)
I have really strange problem. In Visual C++ express, I have very simple code, just:
#include <fstream>
using namespace std;
int main()
{
fstream file;
file.open("test.txt");
file<<"Hello";
file.close();
}
This same code works OK in my one project, but when I create now project and use this same lines of code, no file test.txt is created. Please, what is wrong?ยจ
EDIT: I expect to see test.txt in VS2008/project_name/debug - just like the first functional project does.
Canonical code to write to a file:
#include <fstream>
#include <iostream>
using namespace std;
int main() {
ofstream file;
file.open("test.txt");
if ( ! file.is_open() ) {
cerr << "open error\n";
}
if ( ! ( file << "Hello" ) ) {
cerr << "write error\n";
}
file.close();
}
Whenever you perform file I/O you must test every single operation, with the possible exception of closing a file, which it is not usually possible to recover from.
As for the file being created somewhere else - simply give it a weird name like mxyzptlk.txt and then search for it using Windows explorer.
Perhaps the executable is run in a different directory than it was before, making test.txt appear somewhere else. Try using an absolute path, such as "C:\\Users\\NoName\\Desktop\\test.txt" (The double backslashes are needed as escape characters in C strings).
fstream::open() takes two arguments: filename and mode. Since you are not providing the second, you may wish to check what the default argument in fstream is or provide ios_base::out yourself.
Furthermore, you may wish to check whether the file is open. It is possible that you do not have write permissions in the current working directory (where 'test.txt' will be written since you don't provide an absolute path). fstream provides the is_open() method as one way of checking this.
Lastly, think about indenting your code. While you only have a few lines there, code can soon become difficult to read without proper indentation. Sample code:
#include <fstream>
using namespace std;
int main()
{
fstream file;
file.open("test.txt", ios_base::out);
if (not file.is_open())
{
// Your error-handling code here
}
file << "Hello";
file.close();
}
You can use Process Monitor and filter on file access and your process to determine whether the open/write is succeeding and where on disk it's happening.
Theres two ways to fix this. Either do:
file.open("test.txt", ios::out)
#include <fstream>
using namespace std;
int main()
{
fstream file;
file.open("test.txt", ios::out);
file<<"Hello";
file.close();
}
Or you can create an ofstream instead of fstream.
#include <fstream>
using namespace std;
int main()
{
ofstream file;
file.open("test.txt");
file<<"Hello";
file.close();
}