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.
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.
Unicode strings in UTF-16 format.
Simple char* strings, corresponding to Scheme’s paths.
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
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.
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.
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 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
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.
Similar to the _bytes type, except that a foreign return value of NULL is translated to a Scheme eof value.
Similar to the _string type, except that a foreign return value of NULL is translated to a Scheme eof value.