{ $notes "The appropriate specialized array vocabulary must be loaded; otherwise, an error will be thrown. The vocabulary can be loaded with the " { $link require-c-array } " word. See the " { $vocab-link "specialized-arrays" } " vocabulary for details on the underlying sequence type constructed." } ;
ARTICLE: "c-strings" "C strings"
-"C string types are arrays with shape " { $snippet "{ char* encoding }" } ", where " { $snippet "encoding" } " is an encoding descriptor. The type " { $link char* } " is an alias for " { $snippet "{ char* utf8 }" } ". See " { $link "encodings-descriptors" } " for information about encoding descriptors."
+"C string types are arrays with shape " { $snippet "{ c-string encoding }" } ", where " { $snippet "encoding" } " is an encoding descriptor. The type " { $link c-string } " is an alias for " { $snippet "{ c-string utf8 }" } ". See " { $link "encodings-descriptors" } " for information about encoding descriptors. In " { $link POSTPONE: TYPEDEF: } ", " { $link POSTPONE: FUNCTION: } ", " { $link POSTPONE: CALLBACK: } ", and " { $link POSTPONE: STRUCT: } " definitions, the shorthand syntax " { $snippet "c-string[encoding]" } " can be used to specify the string encoding."
$nl
-"Passing a Factor string to a C function expecting a C string allocates a " { $link byte-array } " in the Factor heap; the string is then converted to the requested format and a raw pointer is passed to the function."
+"Passing a Factor string to a C function expecting a " { $link c-string } " allocates a " { $link byte-array } " in the Factor heap; the string is then converted to the requested format and a raw pointer is passed to the function."
$nl
"If the conversion fails, for example if the string contains null bytes or characters with values higher than 255, a " { $link c-string-error. } " is thrown."
$nl
-"Care must be taken if the C function expects a " { $link char* } " with a length in bytes, rather than a null-terminated " { $link char* } "; passing the result of calling " { $link length } " on the string object will not suffice. This is because a Factor string of " { $emphasis "n" } " characters will not necessarily encode to " { $emphasis "n" } " bytes. The correct idiom for C functions which take a string with a length is to first encode the string using " { $link encode } ", and then pass the resulting byte array together with the length of this byte array."
+"Care must be taken if the C function expects a pointer to a string with its length represented by another parameter rather than a null terminator. Passing the result of calling " { $link length } " on the string object will not suffice. This is because a Factor string of " { $emphasis "n" } " characters will not necessarily encode to " { $emphasis "n" } " bytes. The correct idiom for C functions which take a string with a length is to first encode the string using " { $link encode } ", and then pass the resulting byte array together with the length of this byte array."
$nl
"Sometimes a C function has a parameter type of " { $link void* } ", and various data types, among them strings, can be passed in. In this case, strings are not automatically converted to aliens, and instead you must call one of these words:"
{ $subsections
}
"The first allocates " { $link byte-array } "s, and the latter allocates manually-managed memory which is not moved by the garbage collector and has to be explicitly freed by calling " { $link free } ". See " { $link "byte-arrays-gc" } " for a discussion of the two approaches."
$nl
+"The C type " { $link char } { $snippet "*" } " represents a generic pointer to " { $snippet "char" } "; arguments with this type will expect and return " { $link alien } "s, and won't perform any implicit string conversion."
+$nl
"A word to read strings from arbitrary addresses:"
{ $subsections alien>string }
-"For example, if a C function returns a " { $link char* } " but stipulates that the caller must deallocate the memory afterward, you must define the function as returning " { $link void* } ", and call one of the above words before passing the pointer to " { $link free } "." ;
+"For example, if a C function returns a " { $link c-string } " but stipulates that the caller must deallocate the memory afterward, you must define the function as returning " { $snippet "char*" } " and call one of the above words before passing the pointer to " { $link free } "." ;
projects / factor.git / blobdiff