So I am very new to c++ and on an assignment I have for school I am making a program that uses fstream to put in userIds and passwords into a text file and I am not sure why this will not work when trying to confirm that the username and pass are correct
int login()
{
fstream accountFile2;
bool confirm;
string userID;
string accountPass;
string IDConfirm;
string PassConfirm;
accountFile2.open("accountfile.txt",ios::in | ios::out);
cout<<"Login!\n Enter your User ID: "<<endl;
cin>>userID;
cout<<"Please enter your account's password\n";
cin>>accountPass;
accountFile>>IDConfirm;
accountFile>>PassConfirm;
accountFile2.close();
if((userID == IDConfirm) && (accountPass == PassConfirm))
{
confirm = 1;
cout<<"success";
}
else
{
confirm =0;
cout<<"invalid id/pass";
}
return confirm;
}
Assuming accountFile and accountFile2 is a typo, it works for me (and the compiler).
Double check that the file exists and contains right data. Also beware, that std::cin >> variable for variable of type std::string will read only one word (will stop reading when it finds whitespace). If you want to read whole line, use std::getline(std::cin, variable) instead.
Related
//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.
I am writing a program that is to convert text that a user gives. I have tried this method by itself in a test program and it works perfectly; however when I try to implement it into the larger program, the user cannot give the program an input to store. The relevant code is as follows:
int main()
{
string str = "NULL";
int mappings = 0;
readMappings(mappings);
receiveInput(str);
displayInput(mappings, str);
return 0;
}
void readMappings(int &count)
{
ifstream readMappings; // Creates the function "readMappings"
string filename; // Generates the filename variable to search for mapping document
cout << "Enter the filename of the mapping document: ";
cin >> filename; // User enters filename
readMappings.open(filename); // "readMappings" function opens the given mappings document
while (!readMappings.is_open())
{
cout << "Unsble to open file. Please enter a valid filename: "; // If the user enters an invaled filename, the program will ask again
cin >> filename;
readMappings.open(filename);
}
if (readMappings.good()) // Mapping document is successfully opened
{
readMappings >> count; // Reads first line
}
readMappings.close(); // If everything fails in this function, the document will close
}
void receiveInput(string &input)
{
char correctness;
do {
cout << "\nPlease enter the text you would like to be converted to NATO:\n";
getline(cin, input);
cout << "You are about to convert: \"" << input << "\".\nIs this correct? (Y/N)" << endl;
cin >> correctness;
} while (correctness == 'N' || correctness =='n');
}
I thought it may have been the program waiting for another input from the user so I added a variable I assumed it would already fill, but it did not fix my solution. In my opinion, the problem is in the receiveInput function, but I could be wrong. Thanks in advance for any assistance.
Also, I am using function prototypes with correct reference variables.
I see two problems:
1) You're not checking for an EOF condition, after invoking std::getline().
2) You are mixing together both std::getline and the >> operator. Now, there's actually nothing technically wrong with that, but both std::getline and the >> operator have very nuanced semantics, when it comes to error checking and input consuming, that you need to get 100% right, in order to correctly use them together.
Just replace your usage of the >> operator with std::getline, so you're using std::getline exclusively, and make sure to check for fail() or eof(). You will find plenty of examples of how to correctly check for end of file and failure conditions, with std::getline, here on stackoverflow.com.
This function keeps getting called in another function inside a while-loop while valid_office_num is false. The problem is that if the input begins with a digit but is followed by other invalid characters (e.g. 5t) it takes the digit part and accepts that as a valid input. I want it to consider the whole input and reject it so it can ask for another one. I thought I could use getline() but then I cannot use cin.fail(). How could I implement this behavior?
I forgot to mention I am very new to C++, I have only learnt the basics so far.
(To be clear the desired behavior is to reject anything that contains anything other than digits. This is not an integer range check question. If it is NOT an integer, discard it and request another one)
//Function to read a valid office number, entered by user
int read_office_num()
{
//Declaration of a local variable
int office_num;
//Read input
cin >> office_num;
//Check if input was valid
if (cin.fail())
{
//Print error message
cout << "\nInvalid office number, it should only consist of digits!! Enter another:\n";
//Clear error flags
cin.clear();
//Ignore any whitespace left on input stream by cin
cin.ignore(256, '\n');
}
else
{
//Office number entered is valid
valid_office_num = true;
}
return office_num;
}
From what I gather you want the whole line to be read as a number and fail otherwise?
Well, you can use std::getline(), but you have to follow the algorithm below (I will leave the implementation to you..)
use std::getline(cin, str) to read a line, and if this returns true
use std::stoi(str, &pos) to convert to integer and get the position of the last integer
if pos != str.size() then the whole line in not an integer (or if the above throws an exception), then it's not a valid integer, else return the value...
Read a line of input as a std::string using std::getline().
Examine the string and check if it contains any characters that are not digits.
If the string only contains digits, use a std::istringstream to read an integer from the string. Otherwise report a failure, or take whatever other recovery action is needed (e.g. discard the whole string and return to read another one).
You could use a stringstream
int read_office_num()
{
//Declaration of a local variable
int office_num;
string input = "";
while (true) {
getline(cin, input);
stringstream myStream(input);
if (myStream >> office_num)
break;
cout << "\nInvalid office number, it should only consist of digits!! Enter another:\n" << endl;
}
return office_num;
}
If you want to reject input like 123 xxx you could add an additional check to verify that the received string is indeed an integer:
bool is_number(const string& s)
{
string::const_iterator itr = s.begin();
while (itr != s.end() && isdigit(*itr)) ++itr;
return !s.empty() && itr == s.end();
}
int read_office_num()
{
//Declaration of a local variable
int office_num;
string input = "";
while (true) {
getline(cin, input);
stringstream myStream(input);
if (is_number(input) && myStream >> office_num)
break;
cout << "\nInvalid office number, it should only consist of digits!! Enter another:\n" << endl;
}
return office_num;
}
You should probably just look at the number of input characters that are left in cin. You can do that with in_avail
Your function will probably end up having a body something like this:
//Declaration of a local variable
int office_num;
//Read input and check if input was valid
for (cin >> office_num; cin.rdbuf()->in_avail() > 1; cin >> office_num){
//Print error message
cout << "\nInvalid office number, it should only consist of digits!! Enter another:\n";
//Ignore any whitespace left on input stream by cin
cin.ignore(std::numeric_limits<std::streamsize>::max(), '\n');
}
//Office number entered is valid
valid_office_num = true;
return office_num;
Points of interest:
There is always at least 1 character in cin otherwise the cin would be marked as bad and that would not be good
You don't need valid_office_num if read_office_num is implemented this way, cause valid_office_num will always be set to true before returning
Hm. I may be missing something, but why not read a line, trim it, use regular expressions to validate a number and then exploit strstream's facilities or just atoi if you must? In all reality I'd probably just let users get away with extraneous input (but discard it if I'm sure I'm always running interactively). Following the motto "be lenient in what you accept."
The "interactive" caveat is important though. One can generally not assume that cin is a terminal. Somebody may get cocky and let your program run on a text file or in a pipeline, and then it would fail. A robust approach would separate data processing (portable) from means of input (possibly machine specific and therefore also more powerful and helpful than stdin/stdout via a console).
Here's how to do it using Boost Lexical Cast:
#include <boost/lexical_cast.hpp>
#include <iostream>
#include <vector>
#include <string>
int read_office_num()
{
using boost::lexical_cast;
using boost::bad_lexical_cast;
using namespace std;
int office_num;
while (true)
{
try
{
string input = cin.getline();
office_num = lexical_cast<int>(*argv));
break;
}
catch(const& bad_lexical_cast)
{
cout << "\nInvalid office number, it should only consist of digits!! Enter another:\n";
}
}
return office_num;
}
I am trying to figure out how to correctly make a File I/O Function in C++, however I can not seem to get it to work properly. I am currently not at the level to use vectors yet.
How would I go about changing this code to make it into a working function?
If anyone could point me in the right direction I would be grateful.
Here is the Prototype:
string obtain_inFileName(void);
The Function Call:
inputFileName = obtain_inFileName();
The Function:
string obtain_inFileName(void)
{
string inFile;
cout<<"Enter the name of the input file: ";
cin >> inFile;
cout << endl;
return (inFile);
}
Well, the closest thing I could consider working for your case would be
string obtain_inFileName (ifstream &inFileName) {
std::string inputFileName;
cout<<"Enter the name of the input file: ";
cin>>inputFileName;
inFileName.open(inputFileName.c_str());
return inputFileName;
}
Not claiming, that this is a good implementation!
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.