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Full Discussion: Read in numbers from console won't stop at newline.
Top Forums Programming Read in numbers from console won't stop at newline. Post 303007988 by yifangt on Friday 24th of November 2017 12:38:45 PM
Old 11-24-2017
Read in numbers from console won't stop at newline.
Hello,
I have snippet code from Lippman's <<C++ primer>>.
The program is to convert regular decimal (0 ~ 15) numbers to basic hexdecimals. The instruction tells the program will execute by hitting newline at the end. When I tried to run the compiled program, hitting ENTER did not work as instructed in the book. I have to hit any invalid letter/key or Ctrl+D (I'm using Ubuntu) to terminate the input.
Code:
#include <iostream>
#include <string>

using namespace std;

int main ()
{
  const string hexdigits = "0123456789ABCDEF";    //All possible hex digits
  cout << "Enter a series of numbers between 0 and 15"
    << " separated by spaces.\nHit ENTER when finished: " << endl;

  string result;        //will hold the resulting hexify-ed string
  string::size_type n;        //hold numbers from the input

  while (cin >> n)
    if (n < hexdigits.size())    //ignore invalid input
      result += hexdigits[n];    //fetch the individual hex digit

  cout << "Your hex number is: " << result << endl;
  return 0;
}

Exact same question was asked in stackoverflow,

Code:
// https://stackoverflow.com/questions/19307979/cin-in-a-while-loop
#include <iostream>
#include <string>
#include <sstream>

using namespace std;

int main ()
{
  const string hexdigits = "0123456789ABCDEF";

  cout <<  "Enter a series of numbers between 0 and 15"
       << " separated by spaces. Hit ENTER when finished: "
       << endl;

  string line;
  string result;

  if (getline (cin, line))    // get the whole line
    {
      istringstream iss(result);    // break them by spaces
      int i;
      while (iss >> i)
    {
      result += hexdigits[i];
      result += " ";
    }
      cout << "Your hex result:  " << result << endl;
    }
  else
    {
      cout << "Error handling input!" << endl;
    }

  return 0;
}

1) which used getline() and I can't get the logic flow and the posted code did not work as expected; and
2) it seems there may be better way for this basic trick.
My question is what is the best practice to stop reading space-delimited numbers at newline instead of Ctrl+D or by hitting any invalid char?
Thanks!
Last edited by yifangt; 01-24-2018 at 05:24 PM.. Reason: typos and reformat
 

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LEARN ABOUT X11R4

gid

GID(1)								   User Commands							    GID(1)

NAME

       gid - Query ID database and report results.

SYNOPSIS

       gid [OPTION]... PATTERN...

DESCRIPTION

       Query  ID database and report results.  By default, output consists of multiple lines, each line containing the matched identifier followed
       by the list of file names in which it occurs.

       -f, --file=FILE
	      file name of ID database

       -i, --ignore-case
	      match PATTERN case insensitively

       -l, --literal
	      match PATTERN as a literal string

       -r, --regexp
	      match PATTERN as a regular expression

       -w, --word
	      match PATTERN as a delimited word

       -s, --substring
	      match PATTERN as a substring

	      Note: If PATTERN contains extended regular expression metacharacters, it is interpreted as a regular expression  substring.   Other-
	      wise, PATTERN is interpreted as a literal word.

       -k, --key=STYLE
	      STYLE is one of `token', `pattern' or `none'

       -R, --result=STYLE
	      STYLE is one of `filenames', `grep', `edit' or `none'

       -S, --separator=STYLE
	      STYLE is one of `braces', `space' or `newline' and only applies to file names when `--result=filenames'

	      The above STYLE options control how query results are presented.	Defaults are --key=token --result=filenames --separator=space

       -F, --frequency=FREQ
	      find tokens that occur FREQ times, where FREQ is a range expressed as `N..M'.  If N is omitted, it defaults to 1, if M is omitted it
	      defaults to MAX_USHRT

       -a, --ambiguous=LEN
	      find tokens whose names are ambiguous for LEN chars

       -x, --hex
	      only find numbers expressed as hexadecimal

       -d, --decimal
	      only find numbers expressed as decimal

       -o, --octal
	      only find numbers expressed as octal

	      By default, searches match numbers of any radix.

       --help display this help and exit

       --version
	      output version information and exit

REPORTING BUGS

       Report bugs to bug-idutils@gnu.org

SEE ALSO

       The full documentation for gid is maintained as a Texinfo manual.  If the info and gid programs are properly installed at  your	site,  the
       command

	      info gid

       should give you access to the complete manual.

gid - 4.5							    August 2010 							    GID(1)
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