3.4 String Types

3.4.1 Primitive String Types

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

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

_string/ucs-4 : ctype?

A type for Scheme’s native Unicode strings, which are in UCS-4 format. These correspond to the C mzchar* type used by PLT Scheme.

_string/utf-16 : ctype?

Unicode strings in UTF-16 format.

_path : ctype?

Simple char* strings, corresponding to Scheme’s paths.

_symbol : ctype?

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

3.4.2 Fixed Auto-Converting String Types

_string/utf-8 : ctype?

_string/latin-1 : ctype?

_string/locale : ctype?

Types that correspond to (character) strings on the Scheme 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.

_string*/utf-8 : ctype?

_string*/latin-1 : ctype?

_string*/locale : ctype?

Similar to _string/utf-8, etc., but accepting a wider range of values: Scheme byte strings are allowed and passed as is, and Scheme 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 Scheme 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 Scheme strings and char* strings using a parameter-determined conversion.

_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.

(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

_file : ctype?

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

_bytes/eof : ctype?

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

_string/eof : ctype?

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