Input File problems: input_file.fail() is true and idk why - c++

My code is supposed to open a file and work with the data that it reads in. My code looks like this:
#include <iostream>
#include <iomanip>
#include <fstream>
using namespace std;
int main()
{
ifstream input_file;
input_file.open("practice.txt");
if (input_file.fail())
{
cout << "Attempt to open file failed." << endl;
}
else
It always returns "attempt to open file failed". I am definitely using the correct file name, so what are some reasons that the file isn't opening?
How do I solve this issue?
EDIT: spoke to another girl in my class with a Mac and her code works perfectly when not run on Mac but won't open the file when she runs it on her computer so I think it's a problem with my compiler. Thanks for the help!!

Related

Ifstream is opening the file, but doesn't output the lines inside the file

Im new to c++ and i was trying to open a ".txt" file using ifstream. the file im using is called "ola.txt" which literally just contains two lines of text without punctuation just plain and simple text. The code that i wrote is this
#include <iostream>
#include <vector>
#include <fstream>
#include <iomanip>
#include <string>
using namespace std;
int main()
{
int x;
string line;
vector<int> vect;
ifstream inFile("C:\\Users\\ruial\\Desktop\\ola.txt");
inFile.open("C:\\Users\\ruial\\Desktop\\ola.txt");
if (inFile.is_open()) {
while (getline(inFile, line))
{
cout << line << '\n';
}
inFile.close();
}
else {
cout << "Unable to open file";
exit(1); // terminate with error
}
return 0;
}
The path to the file that i wrote is correct such that the file opens, but when the program runs it doesn´t cout the lines that i wrote on the txt file to the cmd, i dont know if this is somewhat important but im coding in visual studio 2019.
I can't seem to find the answer to this problem anywhere in the internet and to be honest i think im doing it right, any help would be much appreciated,thanks in advance.
You are trying to open the inFile twice. First time during inFile construction, ifstream inFile("C:\\Users\\ruial\\Desktop\\ola.txt"), second time you try to open it again with inFile.open("C:\\Users\\ruial\\Desktop\\ola.txt"), when it's already open, which is erroneous, and flags the stream as no longer good.
3 possible fixes:
Remove inFile.open("C:\\Users\\ruial\\Desktop\\ola.txt")
Use default constructor, without specifying the file name
inFile.close() before you open it again (obviously, not the nicest fix).

CodeBlocks on Mac are not reading file

#include <iostream>
#include <fstream>
using namespace std;
int main()
{
int A;
ifstream file("file.txt"); // there is a single "8" in the file
file >> A;
cout << A; // I get 0 always
return 0;
}
While I'm not new to CodeBlocks, I'm new to CodeBlocks on Mac. I have changed the "Execution working directory" and it still does not work, please help.
Don't change the execution working directory.. When you're reading from file, try writing the full directory where is that file, for example:
// this is your file.txt location
ifstream file("C:\\Desktop\\file.txt"); // this is for Windows
and then run a program.
If it still doesn't work, try watching this tutorial: https://www.youtube.com/watch?v=De6trY8FRYY

C++ ifstream will not open any files

Whenever I try to open a file with ifstream, it compiles fine, but will not open the file.
The file in this example doesn't exist, but ifstream *s*should*s* create the file for me.
i have some example code that i think should work, but does not open or create the file
"foo.txt". Is there something that i'm missing, or is my IDE just messed up?
i'm using visual studio 2008 VC++ , btw
thanks
here's the code:
#include <stdio.h>
#include <iostream>
#include <fstream>
#include <string>
using namespace std;
int main(){
ifstream in;
string hold;
in.open("foo.txt",ios::in);
if(!in){
cerr << "Couldn't open file!" << endl;
}
in >> hold;
cout << hold << endl;
system("pause");
return 0;
}
The problem is you are using an in stream instead of an out stream, as Adam Liss mentioned(ios::out rather than ios::in). You also need to make sure you close the file before return 0; to make sure everything from the buffer is actually written to the file.
The open function will not create files in ios::in mode; you need to use ios::out.

VS C++ program only works when .exe is run from folder? [not VS debug]

Output from debug:
File opened...
File contents:
Output from .exe (run via double click from /project/debug):
File opened...
File contents:
line1
line2
etc. . .
Source code:
#include <iostream>
#include <fstream>
#include <regex>
#include <string>
#include <list>
using namespace std;
using namespace tr1;
int main()
{
string line;
list<string> dataList;
ifstream myFile("test_data.txt");
if (! myFile)
{
cout << "Error opening file. \n";
return 0;
}
else
{
cout << "File opened... \n";
while( getline(myFile, line) ) {
dataList.push_back(line);
}
}
cout << "\n\n File contents:";
list<string>::iterator Iterator;
for(Iterator = dataList.begin();
Iterator != dataList.end();
Iterator++)
{
cout << "\t" + *Iterator + "\n";
}
getchar();
return 1;
}
thank you for your help!
i now understand the problem, thank you. obviously, this also shows that this method of error handling for files is worthless. I have corrected that as well. Thanks again.
The way you've coded this line:
ifstream myFile("test_data.txt");
means that the code is looking for the file in the current working directory.
When you run outside the debugger that will be /project/debug (in your case), which is where the file presumably is.
When you run inside the debugger that will (probably) be \project, which won't contain the file.
You'll need to either have two copies of the file, hard code the full path to the file, or have some way of specifying the file at runtime.
You can also specify the working directory (where it will look for test_data.txt) in the Debug property page for your project in VC.
Your .exe is normally run from Debug/../ when started from Visual Studio. When you double-click on it, it runs in 'Debug/'.
Either move your test_data.txt, or do as most developers and create an output directory where your binaries and data are exported before run.

Problem with file stream/fstream in Xcode C++

Here is a simple program to output to a text file:
#include <iostream>
#include <fstream>
using namespace std;
int main() {
double myNumber = 42.5;
fstream outfile("test.txt", fstream::out);
outfile << "The answer is almost " << myNumber << endl;
outfile.close();
}
All that ends up being wrote to my text file is, "The answer is almost " and the data is not displayed at all. What am I doing wrong? or could it be a problem with Xcode since I am using that as an IDE.
I'm not sure what the problem is. Is it that it's never executed or that it's writing to the wrong path. To shed light on this try include unistd.h and insert this snippet.
char* s = getcwd(NULL, 256);
printf("im running and pwd is: %s\n", s);
Inside xcode hit CMD-SHIFT-R to open the console and see if it prints anything.
There is no problem with your code. It could be a problem with Xcode.