Reading Vector string [duplicate] - c++

Question

This question already has answers here:
Why does std::getline() skip input after a formatted extraction?
(5 answers)
Closed 2 years ago.
I need the following program to take the entire line of user input and put it into string names:
cout << "Enter the number: ";
int number;
cin >> number;
cout << "Enter names: ";
string names;
getline(cin, names);
With the cin >> number command before the getline() command however (which I'm guessing is the issue), it won't allow me to input names. Why?
I heard something about a cin.clear() command, but I have no idea how this works or why this is even necessary.

Answer 1

cout << "Enter the number: ";
int number;
cin >> number;
cin.ignore(256, '\n'); // remaining input characters up to the next newline character
// are ignored
cout << "Enter names: ";
string names;
getline(cin, names);

Answer 2

Another way of doing it is to put a
cin.ignore ( std::numeric_limits<std::streamsize>::max(), '\n' );
after your cin>>number; to flush the input buffer completely (rejecting all of the extra characters until a newline is found). You need to #include <limits> to get the max() method.

Answer 3

cout << "Enter the number: ";
int number;
if (cin >> number)
{
// throw away the rest of the line
char c;
while (cin.get(c) && c != '\n')
if (!std::isspace(c))
{
std::cerr << "ERROR unexpected character '" << c << "' found\n";
exit(EXIT_FAILURE);
}
cout << "Enter names: ";
string name;
// keep getting lines until EOF (or "bad" e.g. error reading redirected file)...
while (getline(cin, name))
...use name...
}
else
{
std::cerr << "ERROR reading number\n";
exit(EXIT_FAILURE);
}
In the code above, this bit...
char c;
while (cin.get(c) && c != '\n')
if (!std::isspace(c))
{
std::cerr << "ERROR unexpected character '" << c << "' found\n";
exit(EXIT_FAILURE);
}
...checks the rest of the input line after the number contains only whitespace.
Why not just use ignore?
That's pretty verbose, so using ignore on the stream after >> x is an oft-recommended alternative way to discard content through to the next newline, but it risks throwing away non-whitespace content and in doing so, overlooking corrupt data in the file. You may or may not care, depending on whether the file's content's trusted, how important it is to avoid processing corrupt data etc..
So when would you use clear and ignore?
So, std::cin.clear() (and std::cin.ignore()) isn't necessary for this, but is useful for removing error state. For example, if you want to give the user many chances to enter a valid number.
int x;
while (std::cout << "Enter a number: " &&
!(std::cin >> x))
{
if (std::cin.eof())
{
std::cerr << "ERROR unexpected EOF\n";
exit(EXIT_FAILURE);
}
std::cin.clear(); // clear bad/fail/eof flags
// have to ignore non-numeric character that caused cin >> x to
// fail or there's no chance of it working next time; for "cin" it's
// common to remove the entire suspect line and re-prompt the user for
// input.
std::cin.ignore(std::numeric_limits<std::streamsize>::max());
}
Can't it be simpler with skipws or similar?
Another simple but half-baked alternative to ignore for your original requirement is using std::skipws to skip any amount of whitespace before reading lines...
if (std::cin >> number >> std::skipws)
{
while (getline(std::cin, name))
...
...but if it gets input like "1E6" (e.g. some scientist trying to input 1,000,000 but C++ only supports that notation for floating point numbers) won't accept that, you'd end up with number set to 1, and E6 read as the first value of name. Separately, if you had a valid number followed by one or more blank lines, those lines would be silently ignored.

Answer 4

Try:
int number;
cin >> number;
char firstCharacterOfNames;
cin >> firstCharacterOfNames; // This will discard all leading white space.
// including new-line if there happen to be any.
cin.unget(); // Put back the first character of the name.
std::string names;
std::getline(cin, names); // Read the names;
Alternatively. If you know that number and names will always be on different lines.
cin >> number;
cin.ignore(std::numeric_limits<std::streamsize>::max(), '\n');
std::getline(cin, names);

Answer 5

You can use std::ws to extract any whitespace characters in the input buffer before using getline. Header for std::ws is sstream.
cout << "Enter the number: ";
int number;
cin >> number;
cout << "Enter names: ";
string names;
cin>>ws;
getline(cin, names);

Answer 6

Try cin.ignore() when you use cin before getline() function
void inputstu(){
cout << "Enter roll Number:";
cin >> roll_no;
cin.ignore(); //ignore the withspace and enter key
cout << "Enter name:";
getline(cin, stu_name);
}

Answer 7

Or you can flush the input buffer to read the string
fflush(stdin)
it is defined in header stdio.h.
This code works..
cout << "Enter the number: ";
int number;
cin >> number;
cout << "Enter names: ";
string names;
fflush(stdin); //FLUSHING STDIN
getline(cin, names);

Answer 8

i just used
getline(cin >> ws,lard.i_npute);
with the standard
#include <iostream>
header in the instances where I was having problems with carriage returns and the ws manipulator worked. I will probably start embedding looping functions as classes and using constructor and destructor calls atleast.

Answer 9

cout << "Enter the number: ";
int number;
cin >> number;
cout << "Enter names: ";
string names;
getline(cin, names);//works on the \n left behind
getline(cin, names);//continues and rewrites names
its pretty self explainatory, there is a \n left behind in the stream that cin >> number uses, which gets assigned to names the first time its used. Reusing the getline writes the correct value now.

Answer 10

You can find the answer you want in cppreference.
When used immediately after whitespace-delimited input, e.g. after int n; std::cin >> n;, getline consumes the endline character left on the input stream by operator>>, and returns immediately. A common solution is to ignore all leftover characters on the line of input with cin.ignore(std::numeric_limits<std::streamsize>::max(), '\n'); before switching to line-oriented input.

Answer 11

you want to use cin.ignore() after your cin statements because you want to ignore the "\n" left in the buffer after taking your int variable with cin.
i have a similar program i used with a similar problem:
#include <iostream>
#include <iomanip>
#include <limits>
using namespace std;
int main() {
int i = 4;
double d = 4.0;
string s = "HackerRank ";
// Declare second integer, double, and String variables.
int n;
double d2;
string str;
// Read and save an integer, double, and String to your variables.
cin >> n;
cin >> d2;
cin.ignore();
getline(cin, str);
// Print the sum of both integer variables on a new line.
cout << i + n << endl;
// Print the sum of the double variables on a new line.
cout << d + d2 << endl;
// Concatenate and print the String variables on a new line
cout << s << str << endl;
// The 's' variable above should be printed first.
return 0;
}

Answer 12

Conceptually, I think you want each answer to be neatly one line. So why don't you try this?
cout << "Enter the number: ";
string line;
getline(cin, line);
int number = std::stoi(line);
cout << "Enter names: ";
string names;
getline(cin, names);
The code consumes the first newline character correctly, gives you the number if the line is correct or throws an exception if it is not. All for free!

Answer 13

#include <iostream>
#include <string>
using namespace std;
int main()
{
cout << "Enter the number: ";
int number;
cin >> number;
cout << "Enter names: ";
string names;
// USE peek() TO SOLVE IT! ;)
if (cin.peek() == '\n') {
cin.ignore(1 /*numeric_limits<streamsize>::max()*/, '\n');
}
getline(cin, names);
return 0;
}
Just peek ahead using cin.peek() and see if a '\n' is still left in cin's internal buffer. If so: ignore it (basically skip over it)