如何知道字符串只包含特定的单词

Question

How do I check if the string contains only words in an array?

I could return true if the string contains any word in the array using Contains()

public bool ValidateString(string strCondition)
{
       List<string> words = new List<string>() { "true", "false", "&&", "||", " " };
       foreach (string word in words)
       {
            if(strCondition.Contains(word))
                return true;                
       }
       return false;
}

But how can I return false if the string that is send as parameter( strCondition ) contains any word or alphabet or number or etc etc other than true , false , && , || , ? Is there any option in Regex or can some one come up with a good solution?

EDIT

The following should return true

true && false || false && false
true || false && false && false

And the below should return false since it contains a word/number/special characters other than true , false , && , || ,

true & false || false < false  
true >> false && false && false
true and false 123 false && false
true || false && false xyz false

Answer 1

First, your code suffers from the clbuttic problem : it would return true for a string that has a word "untrue", because the code does not pay attention to word boundaries.

If you would like to check if no other words are contained, split the string, and check each item against the list of "approved" words:

var allApproved = strCondition.Split(' ').All(word => words.Contains(word));

This approach implies that words in words do not contain spaces.

Note that this is not the most efficient approach, although it would work fine for a small list. If the list is very long, switch to a HashSet<string> instead.

Demo.

Answer 2

You could do something like this:

var regex = new Regex(@"(^(true|false|&&|\|\|)$)");

return regex.IsMatch(input);

Answer 3

Here's another answer which seems to be what you originally asked. If i got it right you wanted to know if only sub-strings are in the text which are in the List<string> .

So "untrue" would return false because "un" is not in the list of allowed "words" (better sub-strings). But "truetrue" would be allowed.

Then have a look at this method which looks more cumbersome but it needs to check something different than the accepted answer:

List<string> words = new List<string>() { "false", "true", "||", "&&", " " };

public bool ValidateString(string strCondition)
{
    if(string.IsNullOrWhiteSpace(strCondition)) return true;
    int charIndex = 0;
    while (charIndex < strCondition.Length)
    {
        string wordFound = null;
        foreach (string word in words)
        {
            if (word.Length + charIndex > strCondition.Length) 
                continue;
            string substring = strCondition.Substring(charIndex, word.Length);
            if (word == substring)
            {
                wordFound = word;
                break;
            }
        }
        if (wordFound == null)
            return false;
        else if (charIndex + wordFound.Length == strCondition.Length)
            return true;
        else
            charIndex += wordFound.Length;
    }
    return false;
}

Note that i've re-ordered the list, the longest strings should come first since that's more efficient in the algorithm above.

Two examples to demonstrate what it does:

bool check = ValidateString("truefalse||truetrue"); // true
bool check = ValidateString("truefals||etruetrue"); // false