When working with Tcl's strings in C, you have to consider ''how'' you are working with them.


**Binary Strings**
Binary strings are conceptually sequences of bytes.

Binary strings have their own `Tcl_ObjType` implementation, `bytearray`.

***Consuming a binary string***

To read a binary string, use `Tcl_GetByteArrayFromObj()` to get the byte sequence and length from the string. The [Tcl_Obj] value that you pass in will probably come from an argument or by reading a variable.

***Producing a binary string***

To produce a binary string value for Tcl to use (e.g., as contents of a variable or the result of a command), use `Tcl_NewByteArrayObj()`. You need to give the byte array buffer and length of the byte sequence; Tcl ''will'' copy this.

**Unicode Strings**
Unicode strings are conceptually sequences of [Unicode] characters, i.e., a sequence of values of the type `Tcl_UniChar` (whose size will vary with Tcl versions and build options).

Unicode strings have their own `Tcl_ObjType` implementation, `unicode`.

***Consuming a unicode string***

`Tcl_GetUnicodeFromObj()` is your primary tool as NUL (`\u0000`) characters are definitely possible and legal. Also useful will be `Tcl_GetUniChar()`, `Tcl_GetCharLength()`, `Tcl_GetRange()`.

***Producing a unicode string***

The main tool is `Tcl_NewUnicodeObj()`, but `Tcl_AppendUnicodeToObj()` and `Tcl_AppendObjToObj()` may be helpful too.


**General Strings**
Here, I refer to strings used for things like option names in command arguments and error messages and stack traces; there will be very few non-ASCII characters that you care about as the only ones you are looking for really are ASCII. If you're only working with strings to really interface with Tcl, this is the type of string you probably care about.

In this case, directly accessing the `bytes` field directly is OK, but using `Tcl_GetString()` and `Tcl_GetStringFromObj()` are preferred. If you are creating them, `Tcl_NewStringObj()` and `Tcl_ObjPrintf()` are useful tools. ''Writing'' to a `bytes` field of an object is usually not a good idea, unless you are in the process of creating that object or specifically writing the `updateStringProc` or `setFromAnyProc` implementations of a `Tcl_ObjType`.

General strings do not have a specific `Tcl_ObjType`; they're the information that (in Tcl 8.*) is ''not'' held in type-specific data.