Is there a concept of '\0' in C#?-CodePudding

What I know is that in C and C \0 is used to end the string and then find the length of the string below method is used.

char[] arr = 'Welcome';
for( int i = 0; arr[i] != '\0'; i  ){
  return i;
}

But for C# it does not seems to work. The code below works but basically catches the exception.

Update - Sorry for the confusion

Is the above one just a method to find the length? By comparing it to '\0'

Why does it not work C#? Is there a concept of '\0' in C# string str = "abc";

    int length = 0;
    try
    {
        length = 0;
        for (int i = 0; str[i] != '\0'; i  )
        {
            length  ;

        }
    }
    catch (System.IndexOutOfRangeException)
    {
        Console.WriteLine(length);
        return;
    }

CodePudding user response：

Strings aren't null-terminated in C# (at least visibly; I believe they are internally for the sake of interop, but the termination character occurs outside the bounds of the string itself). The concept of the character '\0' (U 0000) does exist, but it can occur anywhere within a string - there's nothing special about it.

That means that your code to find '\0' does not find the length of the string. (It would also be simpler just to call str.IndexOf('\0') which will return -1 if the string doesn't contain U 0000.)

For example you could have:

string str = "a\0b";

That is a string of length 3 - but your code would claim it had a length of 1.

Just use the Length property to determine the length of a string (in UTF-16 code units; not necessarily Unicode characters). The length is stored in the String object separately from the text data; the Length property accesses it directly rather than having to iterate over the data.

CodePudding user response：

To provide some more information, there are two basic methods of storing strings.

C# uses length prefix, i.e. it stores the length of the string separate from the string itself. This uses slightly more memory than using a terminating character, but has shown to be less error prone than null terminated strings.

So accessing the length is as simple as reading a property: myString.Length

There is no 'finding the length of string' anymore than there is 'finding the length of an array'. The language guarantees that the length-property matches the actual length.

In some cases it can be useful to express strings as Span<char>, since this allows creation of substrings without any copying, but again, the length of the span is stored as a part of the span, and does not rely on any terminating characters.

CodePudding user response：

Internally, there is a concept of NUL-termination of C# strings.

This is an implementation detail which is there only to provide efficient marshalling of strings when using P/Invoke or the like. Since many C/C libraries expect their strings to be NUL-terminated, by NUL-terminating ALL strings in memory, the CLR allows strings to be passed to a C/C function by simply pinning them - they don't need to be copied to a new temporary buffer with an extra NUL at the end.

However, in normal use you would NEVER need to be aware of this - the .Length property of a string always provides the correct string length.

Note that the NUL-termination of strings is also observable when you use unsafe code to access a string, like so:

unsafe
{
    string tenChars = "1234567890";
    int count = 0;

    fixed (char* pStr = tenChars)
    {
        char* p = pStr;

        while (*p   != '\0')
              count;
    }

    Console.WriteLine(count); // Prints 10
}

Note that this does NOT throw an exception - it allows you to access the value one beyond the length of the string. Also note that using fixed to obtain a pointer to a string does NOT make a copy of the string and add a NUL-terminator to it. It points directly to the unchanged string in memory.

Having said all that, the ONLY time you need to worry about or be aware of this implementation detail is when using P/Invoke or using very low-level unsafe code.

The Microsoft documentation is a bit opaque about this.

From https://docs.microsoft.com/en-us/dotnet/csharp/programming-guide/strings/

There's no null-terminating character at the end of a C# string; therefore a C# string can contain any number of embedded null characters ('\0'). The Length property of a string represents the number of Char objects it contains, not the number of Unicode characters.

That's not strictly true, as the unsafe code above proves.

From https://docs.microsoft.com/en-us/dotnet/csharp/language-reference/language-specification/unsafe-code

A char* value produced by fixing a string instance always points to a null-terminated string. Within a fixed statement that obtains a pointer p to a string instance s, the pointer values ranging from p to p s.Length ‑ 1 represent addresses of the characters in the string, and the pointer value p s.Length always points to a null character (the character with value ‘\0’).