Why is the length of this string longer than the number of characters in it?

Question

This code:

string a = \"abc\";
string b = \"A         


        

Answer 1

As the other answers have pointed out, even if there are 3 visible character they are represented with 4 char objects. Which is why the Length is 4 and not 3.

MSDN states that

The Length property returns the number of Char objects in this instance, not the number of Unicode characters.

However if what you really want to know is the number of "text elements" and not the number of Char objects you can use the StringInfo class.

var si = new StringInfo("A                                                                    

                                                        
            

Answer 2

This is because length() only works for Unicode code points that are no larger than U+FFFF. This set of code points is known as the Basic Multilingual Plane (BMP) and uses only 2 bytes.

Unicode code points outside of the BMP are represented in UTF-16 using 4 byte surrogate pairs.

To correctly count the number of characters (3), use StringInfo

StringInfo b = new StringInfo("A                                                                    

                                                        
            

Answer 3

Everyone else is giving the surface answer, but there's a deeper rationale too: the number of "characters" is a difficult-to-define question and can be surprisingly expensive to compute, whereas a length property should be fast.

Why is it difficult to define? Well, there's a few options and none are really more valid than another:

• The number of code units (bytes or other fixed size data chunk; C# and Windows typically use UTF-16 so it returns the number of two-byte pieces) is certainly relevant, as the computer still needs to deal with the data in that form for many purposes (writing to a file, for example, cares about bytes rather than characters)

• The number of Unicode codepoints is fairly easy to compute (although O(n) because you gotta scan the string for surrogate pairs) and might matter to a text editor.... but isn't actually the same thing as the number of characters printed on screen (called graphemes). For example, some accented letters can be represented in two forms: a single codepoint, or two points paired together, one representing the letter, and one saying "add an accent to my partner letter". Would the pair be two characters or one? You can normalize strings to help with this, but not all valid letters have a single codepoint representation.

• Even the number of graphemes isn't the same as the length of a printed string, which depends on the font among other factors, and since some characters are printed with some overlap in many fonts (kerning), the length of a string on screen is not necessarily equal to the sum of the length of graphemes anyway!

• Some Unicode points aren't even characters in the traditional sense, but rather some kind of control marker. Like a byte order marker or a right-to-left indicator. Do these count?

In short, the length of a string is actually a ridiculously complex question and calculating it can take a lot of CPU time as well as data tables.

Moreover, what's the point? Why does these metrics matter? Well, only you can answer that for your case, but personally, I find they are generally irrelevant. Limiting data entry I find is more logically done by byte limits, as that's what needs to be transferred or stored anyway. Limiting display size is better done by the display side software - if you have 100 pixels for the message, how many characters you fit depends on the font, etc., which isn't known by the data layer software anyway. Finally, given the complexity of the unicode standard, you're probably going to have bugs at the edge cases anyway if you try anything else.

So it is a hard question with not a lot of general purpose use. Number of code units is trivial to calculate - it is just the length of the underlying data array - and the most meaningful/useful as a general rule, with a simple definition.

That's why b has length 4 beyond the surface explanation of "because the documentation says so".

Answer 4

From the documentation of the String.Length property:

The Length property returns the number of Char objects in this instance, not the number of Unicode characters. The reason is that a Unicode character might be represented by more than one Char. Use the System.Globalization.StringInfo class to work with each Unicode character instead of each Char.

Answer 5

As others said, it's not the number of characters in the string but the number of Char objects. The character

Answer 6

Your character at index 1 in "A