C++ Notes: Reading Characters

These notes are written using cin as an example, but they apply to all input streams.

What about whitespace?

The standard input stream (cin) does just what you want when reading integers, floating point etc. It ignores all whitespace (blanks, tabs, etc) that appears in front of a number. But when you're reading characters, you will often want to read whitespace too. For example, here's a little loop to count the number of characters in the input stream.

    char c;
    int  count = 0;
    while (cin >> c) {  // DOESN'T READ WHITESPACE!!!!!
        count++;
    }

The fails to give an accurate count of characters because it ignores all the whitespace characters. There are two solutions.

Use the noskipws I/O manipulator to cause a further cin reads to not ignore whitespace (or until the skipws manipulator is used). Here's that same loop rewritten.
```
    char c;
    cin >> noskipws;    // Stops all further whitespace skipping
    while (cin >> c) {  // Reads whitespace chars now.
        count++;
    }
```
This isn't a bad solution, but if you need to switch back and forth between skipping whitespace and not, I'd choose the next alternative.

Use the cin.get() function.

    char c;
    while (cin.get(c)) {  // Always reads whitespace chars.
        count++;
    }

Read one line with cin.get(...) or cin.getline(...)

   char ca[100];
   . . .
   while (cin.get(ca)) {
      // ca has one input line without crlf and with terminating 0
      . . .
   }

Ignoring input

When an error is encountered, it is often useful to skip all remaining characters on the line. You can do that with:

   cin.ignore(n, c);

where n is the number of characters to skip, and c is the character to skip up to, whichever comes first. For example, to skip to the end of the line,

   cin.ignore(1000, '\n');