This question already has answers here:
Why does std::getline() skip input after a formatted extraction?
(5 answers)
Closed 1 year ago.
I'm trying to figure out why when I read my string using getline() function my string gets empty
#include <bits/stdc++.h>
using namespace std;
int main() {
int n;
cin >> n;
string s;
cin >> s;
getline(cin,s);
cout << s;
}
The getline reads characters from an input stream and places them into a string.
If you use "cin >> s" and then use getline(cin, s), you should first call cin.ignore() before it.
Because "std::getline()" performs the following:
Calls s.erase()
Extracts characters from input and appends them to s
If no characters were extracted for whatever reason, getline sets failbit and returns.
You should modify your code like below:
string s;
cin >> s;
cin.ignore();
std::getline(std::cin, s);
Related
This question already has answers here:
When and why do I need to use cin.ignore() in C++?
(7 answers)
Closed 2 months ago.
int main()
{
string a, b;
cin >> a;
// cin.ignore(10000, '\n');
getline(cin, b); // in this case, it wouldn't ignore the \n, so it would just terminate without taking the input
cout << a << endl;
cout << b << endl;
}
My question is specifically on why '\n' is left in the input stream, and the rules regarding cin and getline(), regarding white spaces and delimiters.
\n is left in the stream because when a user inputs something with std::cin, they hit enter and a '\n' char gets into the cin buffer. refer
Cause:
When consuming whitespace-delimited input (e.g. int n; std::cin >> n;)
any whitespace that follows, including a newline character, will be
left on the input stream. Then when switching to line-oriented input,
the first line retrieved with getline will be just that whitespace. refer
Solutions:
An explicit extraneous initial call to getline
Removing consecutive whitespace with std::cin >> std::ws
Ignoring all leftover characters on the line of input with
cin.ignore(std::numeric_limitsstd::streamsize::max(), '\n');
This question already has answers here:
Why does std::getline() skip input after a formatted extraction?
(5 answers)
Closed 2 years ago.
#include<bits/stdc++.h>
using namespace std;
int main() {
int test;
cin>>test;
for(int i=0;i<test;i++){
string name;
getline(cin,name);
cout<<name<<"\n";
}
}
input
2
Pratik Patil
Niranjan shirdhone
output:
Pratik Patil
why this code not scanning string for second test case?
When using the std::cin >> test syntax, a newline is always appended at the end as soon as Enter key is pressed. The leading newline inhibits the expected functionality of your program, it follows that it must be skipped or ignored somehow.
That's why std::getline() ignores the input. You need to discard that newline character. A simple solution to that is to call std::cin.ignore() after the the first extraction:
cin >> test;
cin.ignore();
...
This question already has answers here:
Why does std::getline() skip input after a formatted extraction?
(5 answers)
Closed 4 years ago.
#include<vector>
#include<iostream>
using namespace std;
int main(){
int number;
cin>>number;
string s1;
vector<string> lists;
for(int i=0;i<number;i++){
getline(cin,s1);
lists.push_back(s1);
}
for(int i=0;i<number;i++)
cout<<lists[i]<<" ";
}
When I enter 5 (for eg.) as input number, I am only able to enter 4 strings instead of 5. Can anyone help me out?
Thank you.
after the line cin>>number; there is still the newline character \n (because you pressed enter to input the value )in the input buffer, to fix this you add a line with cin.ignore();
int main(){
int number;
cin>>number;
cin.ignore(); // add this line
string s1;
vector<string> lists;
for(int i=0;i<number;i++){
getline(cin,s1);
lists.push_back(s1);
}
for(int i=0;i<number;i++)
cout<<lists[i]<<" ";
}
You are mixing line-based input (getline) and non-line-based input (cin>>number). This causes your first getline call to read an empty string into s1, because the \n in the stream has not yet been consumed.
So lists actually has 5 elements at the end, it's just that your output makes it hard to notice.
In order to prevent the problem, convert everything to line-based input instead. Replace this:
int number;
cin>>number;
With this:
std::string line;
std::getline(std::cin, line);
auto const number = std::stoi(line);
This is a superior solution anyway, because it makes it easier to detect wrong input (when the user enters something other than an integer number for number).
This question already has answers here:
Using getline(cin, s) after cin [duplicate]
(13 answers)
Why does std::getline() skip input after a formatted extraction?
(5 answers)
Closed 6 years ago.
#include<iostream>
#include<cstring>
using namespace std;
int main() {
int t;
cin >> t;
string s;
getline(cin, s);
cout << s;
return 0;
}
As soon as I press the enter key after giving input for t, the program terminates as string takes the newline character as input. What can I do? I cannot output something between these two inputs and an enter after t is mandatory.
The Enter key you press to end the input for t is added to the input buffer. So the first input in the buffer seen by getline is the Enter key and it thinks you have given an empty line.
Use the ignore function to skip past the newline:
std::cin.ignore(std::numeric_limits<std::streamsize>::max(), '\n');
You can also use two std::getline calls, and use e.g. std::stoi to convert the input an int. Or put in an std::istringstream and extract using the normal >> operator.
You may use getline(cin, s) twice. Fist will ignore rest of first line and the second will actually read what you need or better use cin.ignore() with appropriate arguments
This question already has answers here:
Why does std::getline() skip input after a formatted extraction?
(5 answers)
Closed 8 years ago.
Hi guys i am facing an unknown error while taking input from getline.My purpose is to take a number and two strings as input from the user and print the first string.Here is the problem code
#include <iostream>
using namespace std;
int main() {
int t;
cin>>t;
while(t--)
{ string s,p;
getline(cin,s);
getline(cin,p);
cout<<s;
}
return 0;
}
Now when i give input like:
1
abababa abb
b
it doesn’t print anything.Why is it happening?
After cin>>t, there is a newline remaining in the stream, then the newline will be assigned to s, so cout<<s seems to print nothing(Actually, it prints a newline).
add cin.ignore(100, '\n'); before first getline to ingore the newline.
Each time you use cin to get something like in cin >> t, it will leave a newline in the input buffer. so in next operation it will be affected by that and will seem to skip the "wait for return key" and hence abnormality. To avoid that usecin::ignore.
the documentation says:
Extracts characters from the input sequence and discards them, until
either n characters have been extracted, or one compares equal to
delim.
The function also stops extracting characters if the end-of-file is
reached. If this is reached prematurely (before either extracting n
characters or finding delim), the function sets the eofbit flag.
I have written your code in very understandable way but working
Let me know if you have any issue
#include <iostream>
using namespace std;
int main() {
int t=0;
cout<<"Enter t\n";
cin>>t;
cin.ignore();
while(t>0)
{ string s,p;
cout<<"Enter s\n";
getline(cin,s);
cout<<"Enter p\n";
getline(cin,p);
cout<<" Values s:"<<s<<" p:"<<p<<"\n";
t--;
}
return 0;
}
The newline from cin >> t; after pressing enter is still in std::cin when getline(cin,s) is called, resulting in s being empty. The string you enter is actually being stored in p. Try using a different capture method or flushing the cin buffer before using it again.
I think it's because getline() doesn't ignore the new line ccharacter, but it reads it in the next call yo getline. Try yo put a getline() before each calle, something like this:
Int main() {
int t;
cin>>t;
string s,p;
getline(cin,s);
while(t--)
{
getline(cin,s);
getline(cin, p);
getline(cin,p);
cout<<s;
}
Hope it helps :)