Does getline() not extract the delimiter?

c++ getline delimiter
c++ read line from stdin
when does getline fail
c++ ifstream getline
c++ getline from file into string
getline c++
c getline
cstring getline

So I was taking input some integers and then taking input some sentences.

This code works fine:

#include<bits/stdc++.h>
using namespace std;
main(){
    int c,b,n,i;string s;
    cin>>n>>b>>c;
    for(i=0;i<n;i++){
        cin>>ws;
        getline(cin,s,'\n');
        cout<<s; 
     }
    }

Example:

3 3 3
This is weird
This is weirdDefinitely makes
Definitely makesNo sense
No sense

However, when I try to omit the cin>>ws inside the forloop, it doesn't work properly, eg this code segment,

#include<bits/stdc++.h>
using namespace std;
main(){
    int c,b,n,i;string s;
    cin>>n>>b>>c;
    for(i=0;i<n;i++){
            getline(cin,s,'\n');
            cout<<s;
    }
}

Example:

3 3 3
This is weird
This is weirdDefinitely makes
Definitely makes

..and terminates there instead of taking all three inputs. Why is that? cin>>ws extracts all whitespace from the input but isn't getline() doing that too? So why does it not work properly when I omit cin>>ws in the forloop?

std::getline() extract characters until it extracted the first delimiter character (by default '\n'). The delimiter is not stored in the result but it is extracted. It does not extract whitespace in general or multiple delimiter characters.

As an aside: always check whether input works after trying to read a value.

In the example printed, the issue is is that after formatted input, i.e., using the >> operator, whitespaces are not extracted. That is, the first calls to std::getline() extracts the empty string terminated by the initial newline. It generally is necessary to extract trailing whitespace when switching between formatted and unformatted I/O. That is, You'd want code like

if (cin>>n>>b>>c >> std::ws) {
    for(i=0;i<n;i++){
        if (getline(cin,s,'\n')) {
            cout << "i=" << i << ":'" << s << "'\n";
        }
    }
}

I can't recommend input operations without adding check for success. The output is changed to make it more easily visible what is going on: try the code with/without this particular std::endl to see what is happening.

Problems with getline, () sees this newline character as leading whitespace, and it just stops reading any further. Basically, getline takes a delimiter, which by default is a newline. By setting it as a space the first time, you get rid of the first junk section, using the same method, you get the part you want, and then the final portion goes to the end of the line, also ignoring it.

When you use cin >> it doesn't remove any whitespace after the input. This means the newline that terminated the first 3 inputs is still in the buffer, waiting to be read by the first getline. Since there's nothing before the newline, the first getline delivered an empty string. Your output should have included a newline so you could have seen the empty line, then it would have made sense.

Originally the code you posted showed a cin >> ws just before the for loop which would have eliminated this problem.

getline not working properly ? What could be the reasons?, only and try to output it using cout You will able to print only first word of the string till first white space. 3) If no characters were extracted for whatever reason (not even the discarded delimiter), getline sets failbit and returns. 2) Same as getline ( input, str, input. widen ( ' ' ) ) , that is, the default delimiter is the endline character.

The default delimiter for getline() is '\n', so there is no need to include that in the getline call, though, it should not change the functionality.

See for example Same as getline(input, str, input.widen('\n')), that is, the default delimiter is the endline character.

The change in formatting from the integer input to the getline() input leaves some whitespace (endl) after the integer as explained by @DietmarKühl.

You can change the getline() call to eliminate the delimiter to

getline(cin,s);

which will cause getline() to use '\n' as the default delimiter.

I have modified the 'n' variable to count and removed the other integers to make the code a little simpler to read:

#include <iostream>

int main()
{
    int i;  // index
    int count;  // number of strings to accept
    std::string str;

    std::cout << "Input the number of strings you would like me to process: " << std::endl;
    std::cin >> count;

    if (std::cin >> count >> std::ws) {
        for (i = 0; i < count; i++) {
            if (getline(std::cin, str)) {
                std::cout << "i=" << i << ":'" << str << "'\n";
            }
        }
    }
}

What does cin.getline do in C++?, If the delimiter is found, it is extracted and discarded (i.e. it is not stored and the extract to string #include <iostream> #include <string> int main () { std::string  Yes this is not a CSV file but it is a delimited file so the same approach works. You just have to change , to | where appropriate. – NathanOliver Oct 28 '16 at 11:38

Cin doesn't extract all white spaces, it just gets the first word until the first white space. It is like having a getline with a space delimiter(not quite but close to).

Getline takes the whole line and has the default '\n' delimiter like mentioned above.

Ex:

string a = "Stack Overflow is awesome";

can give you Stack and getline will give you everything at that line

Trying to use int in getline, std::basic_istream<CharT,Traits>& getline( std::basic_istream<CharT as UnformattedInputFunction, except that input.gcount() is not affected. case the delimiter character is extracted from input , but is not appended to str . You cannot use a multiple-character delimiter in getline- it takes a delimiter character(not a delimiter string), hence the compilation error (a string cannot be used where a char is expected). See herefor more info - there's no overload that takes a delimiter string.

getline (string) - C++ Reference, The delimiter is extracted (unlike basic_istream::get()) and counted is counted as an extracted character, an empty input line does not trigger  istream& getline (istream& is, string& str, char delim) : is is the stream from where the function will read the contents. str is the string where it will store the final string. delim is the delimiter or a character that will tell the function to stop reading once it gets this delimiter. istream& getline (istream& is, string& str) :

std::getline - cppreference.com, #include <string> istream& std::getline( istream& is, string& s, char delimiter = '\n' ); The getline() function, which is not part of the string class, reads a line from is you may find that stringstreams are useful in extracting data from that string. In C++, stream classes support line-oriented functions, getline() and write() to perform input and output functions respectively. getline() function reads whole line of text that ends with new line or until the maximum limit is reached. getline() is the member function of istream class and has the syntax:

std::basic_istream<CharT,Traits>::getline, If the delimiter is found, it is extracted and discarded, i.e. it is not stored INPUT_FILE "input.txt" int main() { std::ifstream input(INPUT_FILE); if  The getline() function, which is not part of the string class, reads a line from is and stores it into s. If a character delimiter is specified, then getline() will use delimiter to decide when to stop reading data. For example, the following code reads a line of text from stdin and displays it to stdout:

Comments
  • What is the actual problem: in what way does the code with uses of std::ws not work as expected?
  • Are you redirecting input from a file or actually typing at the console?
  • @DietmarKühl the problem is if I omit cin>>ws inside the forloop, it doesn't take input properly, why is that?
  • @MarkRansom typing in the console
  • What does "it doesn't take input properly" mean? Ideally, provide input and expected output or, even better, demo the problem using a std::istringstream.
  • Clears it up. Thanks :D
  • That is actually incorrect: getline() has two reason to stop: either the delimiter is found or the end of the stream is found. It doesn't stop on newline if it isn't the used delimiter.
  • Changed, same thing happens.
  • Re: " cin just extracts the word" -- std::cin doesn't extract anything. >> and getline extract characters from an input stream; when you pass std::cin to those functions they extract characters from it.