Is string actually an array of chars or does it just have an indexer?

Question

As the following code is possible in C#, I am intersted whether string is actually an array of chars:

string a=\"TEST\";
char C=a[0]; // will be T
         


        

Answer 1

To add a little to Scott Dorman's and Gufa's answer. If you use Windbg and !DumpObject on the string 'abcd' you'll get somthing like this.

0:000> !do 01139b24
Name: System.String
MethodTable: 79330a00
EEClass: 790ed64c
Size: 26(0x1a) bytes
 (C:\WINDOWS\assembly\GAC_32\mscorlib\2.0.0.0__b77a5c561934e089\mscorlib.dll)
String: abcd
Fields:
      MT    Field   Offset                 Type VT     Attr    Value Name
79332c4c  4000096        4         System.Int32  1 instance        5 m_arrayLength
79332c4c  4000097        8         System.Int32  1 instance        4 m_stringLength
793316e0  4000098        c          System.Char  1 instance       61 m_firstChar
79330a00  4000099       10        System.String  0   shared   static Empty
    >> Domain:Value  00181b38:01131198 <<
79331630  400009a       14        System.Char[]  0   shared   static WhitespaceChars
    >> Domain:Value  00181b38:011318b8 <<

You'll notice its only got three instance fields. m_arrayLength, m_stringLength and m_firstChar. It does not contain an instance System.Char[] The other 2 fields are static shared so every System.String has the same Empty string and WhitespaceChar Char Array.

If you follow that with a DumpByte you'll see the string data (in this case abcd) that's in the heap which of course starts at offset 0x0c (m_firstChar) and is 8 bytes wide (m_stringLength 4 x 2 for unicode).

0:000> db 01139b24 L1A

01139b24  00 0a 33 79 05 00 00 00-04 00 00 00 61 00 62 00  ..3y........a.b.
01139b34  63 00 64 00 00 00 00 00-00 00                    c.d......

If you were to look in the SSCLI you'll see that it, as Scott says, either runs unsafe code and uses pointer techniques to read the data using the m_firstChar and the m_stringLength.