//Prompts user for a file name and stores it
string fileName;
cout << "Enter the file name: ";
cin >> fileName;
ifstream inFile (fileName);
inFile.open(fileName);
//Prompt the user until they give the name of a file that can be opened
bool validFileName = false;
while(validFileName == false)
{
if(inFile.is_open())
{
validFileName = true;
}
else
{
cout << "Please enter a valid file name: ";
cin >> fileName;
ifstream inFile;
inFile.open(fileName);
}
}
//this block prints to the terminal, so it's opening
if(inFile.is_open())
{ cout << "It works! \n"; }
I am trying to create a program that will work with a file, but there needs to be a section that checks to see if the file that the user types in is an actual file that the program can open. I've tried a few different ways to write the while loop, because it needs to keep asking until it receives a valid file. I have the valid file name "input.txt", but even when I type that into the terminal it continues to print the error message. I have tried to type the file name with and without quotes, so I'm not sure what it is caught up on. I know it is opening the file, because I added a second check afterward and it appears that it's opening, so I think it's an issue with how I have the error check statement written?
The problem is that you are using
ifstream inFile;
inFile.open(fileName);
in the loop. The variable in the loop hides the variable of the same name outside the loop. Remove the first of those lines.
FWIW, you can simplify your code to:
ifstream inFile (fileName);
while(!inFile)
{
// Prompt the user until they give the name of a file that can be opened
cout << "Please enter a valid file name: ";
cin >> fileName;
inFile.open(fileName);
}
if(inFile)
{
cout << "It works! \n";
}
In:
ifstream inFile (fileName);
inFile.open(fileName);
The file is opened on the first line.
Reopening it is redundant.
Also in the loop you declare a temporary variable inFile which goes out of stop at the end of the else statement. Make sure to declare it only once at the outmost scope you would like to use it.
Related
I am building an input validation function that takes the input of the user and tries to open that file. and repeats if user is not entering the correct format. the correct format is:
test1.txt
My function works if I write correct format in the first run, but after the second run it keeps printing the error message although I am writing the write format to be opened. I have tried to clear the input "cin" and "filename" after taking the input but it did not work. Any ideas ?
string getFileInput()
{
string filename;
fstream file;
cout << "Please enter the name of the file: ";
getline(cin, filename);
file.open(filename.c_str());
while(!file.is_open())
{
file.clear(); file.ignore();
cout << "File name is incorrect, please enter again: ";
cin.clear(); cin.ignore();
getline(cin, filename);
file.open(filename.c_str());
}
// Extra condition. Empty file
if (file.eof())
{
cout << filename << " is an empty file." << endl;
}
file.close();
return filename;
}
I could reproduce and fix.
The problem is caused by cin.ignore(). According to cppreference:
... the next available character c in the input sequence is delim
So ignore will read the next line, up to the newline, and leave that newline alone. And the following getline can only read an empty string!
By the way, using a non opened fstream (file) for ignore and clear is at least useless and could be harmlfull because those methods are expected to be called on an open stream. And using cin.clear() is useless too and can be harmfull: if for any reason you have a read error (because you reached an end of file for example), you will consistently clear the error condition and try to read again when you should abort.
Finally, the eof condition is only set after a read returned nothing because of the end of file. It is never set when opening an empty file, nor if you could successfully read up to the end of file.
So the function should boil down to:
string getFileInput()
{
string filename;
fstream file;
cout << "Please enter the name of the file: ";
getline(cin, filename);
if (! cin) {
// test the error immediately and before using filename!
cerr << "read error: aborting...\n";
return "";
}
file.open(filename.c_str());
while(!file.is_open())
{
cout << "File name is incorrect, please enter again: ";
getline(cin, filename);
if (! cin) {
// test the error immediately and before using filename!
cerr << "read error: aborting...\n";
return "";
}
file.open(filename.c_str());
}
file.close();
return filename;
}
I'm attempting to create a repeating menu that will allow a user to re-enter a file name if the program is unable to open the file.
Right now it works correctly if I enter the name of an existing file, but if the file doesn't exist it prints the "File not found" then executes the rest of the program. I'm new to file streams and most of the code here was found through references. I'm a bit lost on what exactly is going on and what the best way to handle the situation is. Any guidance would be appreciated.
typedef istream_iterator<char> istream_iterator;
string fileName;
ifstream file;
do {
cout << "Please enter the name of the input file:" << endl;
cin >> fileName;
ifstream file(fileName.c_str());
if (!file) {
cout << "File not found" << endl;
}
} while (!file);
std::copy(istream_iterator(file), istream_iterator(), back_inserter(codeInput));
After constructing the object file will always exist, so your loop condition always fails. Change the condition to whether the file didn't open properly.
do {
...
}
while (!file.is_open())
this code will work.
do {
std::cout << "Please enter the name of the input file:" << std::endl;
std::cin >> fileName;
file = std::ifstream(fileName.c_str());
if (!file) {
std::cout << "File not found" << std::endl;
}
} while (!file);
your error was that you have 2 definition of the file variable.
the variable in while (!file) that is used is the one defined outside the do-while loop, and it is valid state is set to true by default.
In addition to #acraig5075 answer:
Writing a type then a variable name (ifstream file) is to create a new variable. Obviously you know this, but if you use the same name again in, for example, a loop, it makes a new and distinct variable.
ifstream file; // a unique variable
...
do {
...
ifstream file(fileName.c_str()); // another unique variable
...so change the usage inside the loop to:
file.open(fileName.c_str());
I'm trying to get characters from an input file but I can't really get it to work, anyone who could help me on this one? I apologize in advance for the formatting, it confused me.
open_input_and_output_file basically checks whether or not you can open the files and in OTP I'm attempting to get every single character from one file to the other. As I couldn't get it to work I first tried displaying those characters in the console application, but that is also not working.
Any help would be appreciated, I hope the information provided is enough.
bool open_input_and_output_file(ifstream& infile, ofstream& outfile)
{
//Precondition: True
assert(true);
//Postcondition: Inputfile and outputfile have either been opened succesfully or you have been notified of it not opening succesfully.
string inputfile;
string outputfile;
cout<<"\nPlease enter an input-file name (no spaces): ";
cin>>inputfile;
cout<<"NOTE: Input-file name and output-file name can NOT be the same!"<<endl;
cout<<"Please enter an output-file name (no spaces): ";
cin>>outputfile;
if(inputfile != outputfile)
{
cout<<"Input-file name and output-file name are not the same! Good job on reading!"<<endl;
ifstream infile(inputfile.c_str());
if(infile)
cout<<"Input-file: "<<inputfile<<" was opened succesfully!"<<endl;
if(!infile)
cout<<"Inputfile: "<<inputfile<<" could not be opened!"<<endl;
ofstream outfile(outputfile.c_str());
if(outfile)
cout<<"Output-file: "<<outputfile<<" was opened succesfully!"<<endl;
if(!outfile)
cout<<"Outputfile: "<<outputfile<<" could not be opened!"<<endl;
}
else
{
cout<<"Input-file name and output-file name are the same!"<<endl;
cout<<"Opening has failed!"<<endl;
}
return 0;
}
void OTP(ifstream& infile, ofstream& outfile)
{
int choice;
char character;
unsigned int r;
srand(r);
cout<<"\nPlease enter 0 to encrypt or 1 to decrypt: ";
cin>>choice;
if(open_input_and_output_file(infile,outfile))
{
infile.get(character);
cout<<character;
}
}
I would say the error is here
cout<<"Input-file name and output-file name are not the same! Good job on reading!"<<endl;
ifstream infile(inputfile.c_str());
should be
cout<<"Input-file name and output-file name are not the same! Good job on reading!"<<endl;
infile.open(inputfile.c_str());
You make the same mistake with outfile.
ofstream outfile(outputfile.c_str());
should be
outfile.open(outputfile.c_str());
You pass infile and outfile as parameters to your open_input_and_output_file function, but then you declare them again inside the function. So when you open the files you aren't using the streams that were passed to open_input_and_output_file, instead you are using streams that are local to that function. The streams passed to open_input_and_output_file stay closed.
The program is supposed to prompt the user for their username. Upon receiving the username it concatenates it with '.history' to create username.history. Then it opens that file (username.history) and reads the input from it. I am running into a segfault here though. Whenever it opens the file, which is empty because the file doesn't exist, it reads multiple lines and then throws the segfault. I think the problem might stem from how I'm trying to open the file, but I'm not sure. Here is the portion that is causing problems:
// File input and output
ifstream f_in;
ofstream f_out;
// Prompt user for their username.
char username[80];
cout << "Please input your username: " << endl;
cin >> username;
cout << endl;
cout << "Loading history file if it exists." << endl;
// Create file naem and initialize the file line counter to 0.
strcat(username, ".history");
int fcount = 0;
// Open file and read in lines if there are any.
// Place read lines into the command string for use later.
char tmp[50];
f_in.open(username);
while(!f_in.eof()){
f_in >> tmp;
cmd[fcount] = tmp;
fcount++;
}
f_in.close();
Other pertinent info:
cmd is declared as a global variable (char cmd[200][50])
Any help will be greatly appreaciated.
Not sure if it is the only issue, but cmd[fcount] = tmp is wrong. You should use strcpy().
while(f_in.good())
{
f_in >> tmp;
cmd[fcount] = tmp;
fcount++;
}
So i basically need my program to open a file and do something. When the program asks for the user to input the file name, and the user inputs the name of file correctly the first time, the operation works. But if the user typed the name wrong, the program says "invalid name try again" but then it is never able to open the file even if the user types the name correctly. Here's the code:
ifstream read_file(file.c_str());
while(true)
{
if(!(read_file.fail()))
{
...
}
else
{
cout << "Either the file doesn't exist or the formatting of the file is incorrect. Try again.\n>";
}
cin >> file;
ifstream read_file(file.c_str());
}
What is the problem, any thoughts? Thank you
You are redeclaring read_file inside the loop, but the code at the top of the loop always use the read_file outside the loop.
This is what you want instead:
ifstream read_file(file.c_str());
while(true)
{
if(!(read_file.fail()))
{
...
}
else
{
cout << "Either the file doesn't exist or the formatting of the file is incorrect. Try again.\n>";
}
cin >> file;
read_file.open(file.c_str()); /// <<< this has changed
}