53 lines
4.1 KiB
Factor
53 lines
4.1 KiB
Factor
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USING: help.markup help.syntax strings byte-arrays alien libc
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debugger io.encodings.string sequences ;
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IN: alien.strings
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HELP: string>alien
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{ $values { "string" string } { "encoding" "an encoding descriptor" } { "byte-array" byte-array } }
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{ $description "Encodes a string together with a trailing null code point using the given encoding, and stores the resulting bytes in a freshly-allocated byte array." }
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{ $errors "Throws an error if the string contains null characters, or characters not representable in the given encoding." } ;
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{ string>alien alien>string malloc-string } related-words
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HELP: alien>string
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{ $values { "c-ptr" c-ptr } { "encoding" "an encoding descriptor" } { "string/f" "a string or " { $link f } } }
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{ $description "Reads a null-terminated C string from the specified address with the given encoding." } ;
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HELP: malloc-string
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{ $values { "string" string } { "encoding" "an encoding descriptor" } { "alien" c-ptr } }
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{ $description "Encodes a string together with a trailing null code point using the given encoding, and stores the resulting bytes in a freshly-allocated unmanaged memory block." }
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{ $warning "Don't forget to deallocate the memory with a call to " { $link free } "." }
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{ $errors "Throws an error if one of the following conditions occurs:"
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{ $list
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"the string contains null code points"
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"the string contains characters not representable using the encoding specified"
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"memory allocation fails"
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}
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} ;
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HELP: string>symbol
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{ $values { "str" string } { "alien" alien } }
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{ $description "Converts the string to a format which is a valid symbol name for the Factor VM's compiled code linker. By performing this conversion ahead of time, the image loader can run without allocating memory."
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$nl
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"On Windows CE, symbols are represented as UCS2 strings, and on all other platforms they are ASCII strings." } ;
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ARTICLE: "c-strings" "C strings"
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"C string types are arrays with shape " { $snippet "{ \"char*\" encoding }" } ", where " { $snippet "encoding" } " is an encoding descriptor. The type " { $snippet "\"char*\"" } " is an alias for " { $snippet "{ \"char*\" utf8 }" } ". See " { $link "encodings-descriptors" } " for information about encoding descriptors."
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$nl
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"Passing a Factor string to a C function expecting a C string allocates a " { $link byte-array } " in the Factor heap; the string is then converted to the requested format and a raw pointer is passed to the function."
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$nl
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"If the conversion fails, for example if the string contains null bytes or characters with values higher than 255, a " { $link c-string-error. } " is thrown."
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$nl
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"Care must be taken if the C function expects a " { $snippet "char*" } " with a length in bytes, rather than a null-terminated " { $snippet "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 " { $link encode } ", and then pass the resulting byte array together with the length of this byte array."
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$nl
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"Sometimes a C function has a parameter type of " { $snippet "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:"
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{ $subsection string>alien }
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{ $subsection malloc-string }
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"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 " { $link "byte-arrays-gc" } " for a discussion of the two approaches."
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$nl
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"A word to read strings from arbitrary addresses:"
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{ $subsection alien>string }
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"For example, if a C function returns a " { $snippet "char*" } " but stipulates that the caller must deallocate the memory afterward, you must define the function as returning " { $snippet "void*" } ", and call one of the above words before passing the pointer to " { $link free } "." ;
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ABOUT: "c-strings"
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