How can I detect if a string is empty of characters?

Question

How do I determine if the string has any alpha character or not?

In other words, if the string has only spaces in it how do I treat it as an Empty string?

Answer 1

C#:

Empty means (MSDN) The value of this field is the zero-length string, "".

Therefor if you have spaces it will not be empty

private bool IsEmtpyOrContainsAllSpaces(String text)
        {
            int count = 0;
            foreach (char c in text)
            {
                if (c == ' ')
                {
                    count++;
                }
            }
            return (count == text.Length);
        }

Answer 2

Try:

if the_string.replace(" ", "") == "":
    the_string = ""

If your language supports it, using "trim", "strip" or "chomp" to remove leading/trailing whitespace could be good too...

edit: Of course, regular expressions could solve this problem too: the_string.match("[^\s]")... Or a custom function... Or any number of things.

edit: In Caml:

let rec empty_or_space = fun
      [] -> true
    | (x::xs) -> x == ` ` and empty_or_space xs;;

edit: As requested, in LOLPYTHON:

BTW OHAI
SO IM LIKE EMPTY WIT S OK?
    LOL IZ S EMPTIE? DUZ IT HAZ UNWHITESPACE CHAREZ /LOL
    IZ S KINDA LIKE ""?
        U TAKE YEAH

    IZ S LOOK AT EASTERBUNNY OK KINDA NOT LIKE " "?
        U TAKE MEH

    U TAKE EMPTY WIT S OWN __getslice__ WIT CHEEZBURGER AND BIGNESS S OK OK

Answer 3

If you are using .NET, then the string type has a .Trim() method that strips leading and trailing spaces.

Answer 4

if you talking about .Net(C# or vb), then you can Trim() it to remove white spaces.

Answer 5

If you really want to treat a string that only contains spaces as an empty string (which it isn't but that's a different story) just use whatever stripping method your language of choice provides (string.lstrip() and string.rstrip() in Python for example) and check if the resulting string has the length 0.

Answer 6

C++

#include <string>

bool isEmptyOrBlank(const std::string& str)
{
   int len = str.size();
   if(len == 0) { return true; }

   for(int i=0;i<len;++i)
   {
       if(str[i] != ' ') { return false; }
   }
   return true;
}

C

#include <string.h>

int isEmptyOrBlank(const char* str)
{
  int i;
  int len;

  len = strlen(str);

  //String has no characters
  if(len == 0) { return 1; }

  for(i=0;i<len;++i)
  {
     if(str[i] != ' ') { return 0; }
  }

  return 1;
}

Java

boolean isEmptyOrBlank(String str)
{
  int len = str.length();
  if(len == 0) { return true; }

  for (int i = 0; i < len; ++i)
  {
    if (str.charAt(i) != ' ')  { return false; }
  }

  return true;
}

You get the idea, you can do something similar in any language.

Answer 7

In C# you should use String.IsNullOrEmpty.

To treat it as an empty string you can just use "" or string.Empty; To check if its empty there is a .Trim function.

Answer 8

if (s =~ /^\w*$/)

should work, as long as you're using Perl.

Anybody got a LOLCODE version?

Answer 9

This will do the job if you are using .net.

string myStr = "    ";    
string.IsNullOrEmpty(myStr.Trim()));

If you are using .net 3.0 or above then you might like to create an extension method for this that you can use with any string.

namespace StringExtensions
{
    public static class StringExtensionsClass
    {
        public static string IsWhiteSpace(this string s)
        {
            return string.IsNullOrEmpty(s.Trim()));
        }
    }
}

You can then use this like so

string myStr = "    ";
if (myStr.IsWhiteSpace())
    Console.Write("It just whitespace");

Hope that this is what you are after.

Answer 10

The canonical method, regardless of language, is to trim the string (trim functions remove whitespace at the beginning and end of a string) and compare the result to the empty string:

if (trim(myString) == "") {
    // string contains no letters, numbers, or punctuation
}

Not all languages have a native trim function, however. Here's a good, general-purpose one for JavaScript, since I haven't seen a JS example yet:

function trim(str) {
    return str.replace(/^\\s+|\\s+$/g, "");
}

(Check out Steven Levithan's post about JavaScript trim functions for an in-depth comparison.)

Alternatively, you can use a regular expression to test "emptiness":

if (/^\s*$/.test(str)) {
    // string contains no letters, numbers, or punctuation
}

Again, not all languages natively support regular expressions. Check your language documentation.

Answer 11

In Java:

private boolean isEmptyOrWhitespace(String str){

    str = str.replaceAll("\\s+", "");

    return (str.length()==0);

}