I'm trying to write a .dat file using Windows subsystem for Linux, but the fstream library seems to bypass every endline command.
Here is my code:
int main()
{
string fname = "DataSheet.dat";
ofstream fdata (fname.c_str(), ios::out);
fdata << "First line" << endl;
fdata << "Second line" << endl;
fdata.close();
return = 0;
}
I tried substituting << endl with << "\n" and modifying the ofstream command like showed there, but nothing worked; the output was always First lineSecond line instead of First line and Second line on subsequent lines.
Besides, the code works perfectly well when I print the output to video using cout command or when I compile and run it on cygwin.
Is it a problem of Windows subsystem for Linux or am I missing something important?
By a comment.
Try substituting << endl with \r\n
This is due to the differences in the line endings of linux and windows.
In windows you need to add a carriage return and then the new line character.
While in linux there is not need for the carriage return.
The problem comes from the fact that you are compiling for linux so std::endl places the linux version line ending but you are trying to view the output in windows.
Related
#include "stdafx.h"
#include <iostream>
#include <fstream>
#include <string>
using namespace std;
int main()
{
string line = "test";
ifstream myfile("example.txt");
myfile.open("example.txt");
if (myfile.is_open())
{
cout << line << "\n";
cout << "File Opened\n";
getline(myfile, line);
cout << line;
while (getline(myfile, line))
{
cout << line << '\n';
cout << "test";
}
myfile.close();
}
else cout << "Unable to open file";
//return 0;
//getchar();
}
Apologies in advance if this has been answered, but while I've found several answers that are very close to what I need, I can't find an answer to this specific problem.
I'm new to Visual Studio, but have dabbled in c++ in the past. I'm trying to read in data from a text file and (for now) simply print that back out with cout. But, I'm not seeing any results.
At first I figured I just had my txt file in the wrong place - and I did. Initially I would receive the line "Unable to open file", indicating that the file could not be opened. So I moved it around and found out where Visual Studio wanted me to put the file.
So now I successfully see the "File Opened\n" line get printed to the screen, followed by nothing. I thought I might be using getline wrong, but if I replace the file input "myfile" with a "cin" instead, getline will happily read in keyboard input all day, so that's not it either.
So I've put in some test cout statements that print out the value of my string, line. The first one prints out "test" as it should. Then I read in a line of the txt file to that string variable, and when I cout it again I get nothing. It's a blank string.
Also, the line " cout << "test"; " From within the loop does NOT print either. So the loop's not even happening, it seems.
So, as near as I can tell, the program is able to find my textfile, example.txt. But it's not actually seeing the contents within.
The contents of the textfile (and what I'd like the program to print out) are as follows:
"This is the first line
This is the second line
Third
Fourth
Fifth"
Any and all help is much appreciated.
Figured it out.
What went wrong is this line:
ifstream myfile("example.txt");
I don't know exactly why, but since I specify the file to open in the next line down ( myfile.open("example.txt"); ), specifying the filepath in the ifstream declaration caused the issue.
I don't entirely get it, as others have said that the code runs fine for them. But this seems to work, anyway.
If there's any reason why I shouldn't use this solution, please let me know.
you might want to take a look at your file open
"myfile.open("example.txt");" i found if you don't give a file path weird things happen.
myfile.open("c:\test\example.txt");
is the adjustment I made to the code and it work like a dream.
I'm writing a C++ program that parses XML into JSON for a class and it works great when I compile in Visual Studio but behaves strangely when compiled with g++ in Linux.
With a bit of testing, I believe I have tracked the issue down into a difference in the way new lines are handled between the different compilers, here's some of the code I'm using to debug:
while (!fileToRead.eof()) { //Until we have reached the end of the file: ...
cout << endl << "newloop: ";
char c;
fileToRead.get(c);
cout << "read " << c << " ";
if (c != '\n' && c != '\t')
cout << "is a text character.";
}
When I run an executable created in Visual Studio, it outputs the following for new line characters it reads:
newloop: read
newloop: read
newloop: read
newloop: read
When I run it on Linux when compiled with g++, it outputs the following for new line characters it reads:
is a text character.
newloop: read
is a text character.
newloop: read
is a text character.
newloop: read
newloop: read
As you can see, when compiled with g++ there are 2 problems:
The third cout ("is a text character.") runs before the first and seconds couts ('"endl << << "newloop: "' and '"read " << c << "')
The if statement ("if (c != '\n' && c != '\t')") runs even when c is a new line character.
Can anyone explain what's going on here?
You are not parsing the same XML file. Even if it looks the same in a text editor.
My guess is, the one on windows contains CRLF newlines (\r\n or 0x0D 0x0A), the other only contains LF (\n or 0x0A) newlines.
Make sure you have the exact same file on either system, and you'll get the same results.
I am doing some scientific work on a system with a queue. The cout gets output to a log file with name specified with command line options when submitting to the queue. However, I also want a separate output to a file, which I implement like this:
ofstream vout("potential.txt"); ...
vout<<printf("%.3f %.5f\n",Rf*BohrToA,eval(0)*hatocm);
However it gets mixed in with the output going to cout and I only get some cryptic repeating numbers in my potential.txt. Is this a buffer problem? Other instances of outputting to other files work... maybe I should move this one away from an area that is cout heavy?
You are sending the value returned by printf in vout, not the string.
You should simply do:
vout << Rf*BohrToA << " " << eval(0)*hatocm << "\n";
You are getting your C and C++ mixed together.
printf is a function from the c library which prints a formatted string to standard output. ofstream and its << operator are how you print to a file in C++ style.
You have two options here, you can either print it out the C way or the C++ way.
C style:
FILE* vout = fopen("potential.txt", "w");
fprintf(vout, "%.3f %.5f\n",Rf*BohrToA,eval(0)*hatocm);
C++ style:
#include <iomanip>
//...
ofstream vout("potential.txt");
vout << fixed << setprecision(3) << (Rf*BohrToA) << " ";
vout << setprecision(5) << (eval(0)*hatocm) << endl;
If this is on a *nix system, you can simply write your program to send its output to stdout and then use a pipe and the tee command to direct the output to one or more files as well. e.g.
$ command parameters | tee outfile
will cause the output of command to be written to outfile as well as the console.
You can also do this on Windows if you have the appropriate tools installed (such as GnuWin32).
I have some issue when I want to print out \n I'm using endl for that. And the problem is when I run the code on Windows7 it won't print out the newline. But it will print out newline in Ubuntu. Both OS is using the same compiler GNU g++.
So I wonder if there are some different way to print newline to file in Windows?
void translate(ofstream &out, const string &line, map<string, string> m)
{
stringstream ss(line);
string word;
while(ss >> word)
{
if(m[word].size() == 0)
out << "A";
else
out << m[word] << " ";
}
out << "\n";
}
Outputting either '\n' or using endl will result in the exact same content (the only difference is endl also flushes). When that \n character is written, if the file is in "text mode", the runtime library converts it to the platform's native mechanism to indicate lines. On unix, this is unnecessary because that mechanism is a \n byte. On Windows, that \n becomes \r\n (carriage return, line feed). I suspect you know all of this, but I'm reviewing it just in case.
In short, as long as your runtime library is setup for Windows, the code you have will work as you expect. I suspect you are using cygwin's g++, or some other g++ port, that is not setup for Windows-style lines, even in text mode. Some editors will not correctly interpret that untranslated \n.
Here is my code:
#include <iostream>
#include <stdlib.h>
#include <fstream>
using namespace std;
int main() {
string line;
ifstream inputFile;
inputFile.open("input.txt");
do {
getline(inputFile, line);
cout << line << endl;
} while (line != "0");
return 0;
}
input.txt content:
5 9 2 9 3
8 2 8 2 1
0
In Enclipse, it goes to infinite-loop. I'm using MinGW 5.1.6 + Eclipse CDT.
I tried many things but I couldn't find the problem.
Since you are on windows try:
} while (line != "0\r");
The last line is stored as "0\r\n". The \n is used as the line delimiter by getline so the actual line read will be "0\r"
or
you can convert the dos format file to UNIX format using command
dos2unix input.txt
Now your original program should work. The command will change the \r\n at the end of the line to \n
Also you should always do error checking after you try to open a file, something like:
inputFile.open("input.txt");
if(! inputFile.is_open()) {
cerr<< "Error opening file";
exit(1);
}
It will create an infinite loop if no line contains exactly 0. For example 0\n is not the same thing as 0. My guess is that that is your problem.
EDIT: To elaborate, getline should be discarding the newline. Perhaps the newline encoding of your file wrong (i.e. windows vs. unix).
Your main problem is working directory.
Because you are specifying a file using a relative path it searches for the file from the current working directory. The working directory can be specified by your dev environment. (Note: The working directory is not necessarily the same directory where the executable lives (this is a common assumption among beginners but only holds in very special circumstances)).
Though you have a special end of input marker "0" you should also check that the getline() is not failing (as it could error out for other reasons (including beady formatted input). As such it is usually best to check the condition of the file as you read it.
int main()
{
string line;
ifstream inputFile;
inputFile.open("input.txt");
while((getline(inputfile, line)) && (line != "0"))
{
// loop only entered if getline() worked and line !="0"
// In the original an infinite loop is entered when bad input results in EOF being hit.
cout << line << endl;
}
if (inputfile)
{
cout << line << endl; // If you really really really want to print the "0"
// Personally I think doing anything with the termination
// sequence is a mistake but added here to satisfy comments.
}
return 0;
}