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3.4.1 Primitive String Types
_  string/  ucs-4
_  string/  utf-16
_  path
_  symbol
3.4.2 Fixed Auto-Converting String Types
_  string/  utf-8
_  string/  latin-1
_  string/  locale
_  string*/  utf-8
_  string*/  latin-1
_  string*/  locale
3.4.3 Variable Auto-Converting String Type
_  string
default-_  string-type
3.4.4 Other String Types
_  file
_  bytes/  eof
_  string/  eof

3.4 String Types

3.4.1 Primitive String Types

The five primitive string types correspond to cases where a C representation matches Racket’s representation without encodings.

The form _bytes form can be used type for Racket byte strings, which corresponds to C’s char* type. In addition to translating byte strings, #f corresponds to the NULL pointer.

A type for Racket’s native Unicode strings, which are in UCS-4 format. These correspond to the C mzchar* type used by Racket. As usual, the types treat #f as NULL and vice versa.

Unicode strings in UTF-16 format. As usual, the types treat #f as NULL and vice versa.

value

_path : ctype?

Simple char* strings, corresponding to Racket’s paths. As usual, the types treat #f as NULL and vice versa.

Beware that changing the current directory via current-directory does not change the OS-level current directory as seen by foreign library functions. Paths normally should be converted to absolute form using path->complete-path (which uses the current-directory parameter) before passing them to a foreign function.

value

_symbol : ctype?

Simple char* strings as Racket symbols (encoded in UTF-8). Return values using this type are interned as symbols.

3.4.2 Fixed Auto-Converting String Types

Types that correspond to (character) strings on the Racket side and char* strings on the C side. The bridge between the two requires a transformation on the content of the string. As usual, the types treat #f as NULL and vice versa.

Similar to _string/utf-8, etc., but accepting a wider range of values: Racket byte strings are allowed and passed as is, and Racket paths are converted using path->bytes.

3.4.3 Variable Auto-Converting String Type

The _string/ucs-4 type is rarely useful when interacting with foreign code, while using _bytes is somewhat unnatural, since it forces Racket programmers to use byte strings. Using _string/utf-8, etc., meanwhile, may prematurely commit to a particular encoding of strings as bytes. The _string type supports conversion between Racket strings and char* strings using a parameter-determined conversion.

value

_string : ctype?

Expands to a use of the default-_string-type parameter. The parameter’s value is consulted when _string is evaluated, so the parameter should be set before any interface definition that uses _string.

parameter

(default-_string-type)  ctype?

(default-_string-type type)  void?
  type : ctype?
A parameter that determines the current meaning of _string. It is initially set to _string*/utf-8. If you change it, do so before interfaces are defined.

3.4.4 Other String Types

value

_file : ctype?

Like _path, but when values go from Racket to C, cleanse-path is used on the given value. As an output value, it is identical to _path.

Similar to the _bytes type, except that a foreign return value of NULL is translated to a Racket eof value.

Similar to the _string type, except that a foreign return value of NULL is translated to a Racket eof value.