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Article contents:== Outdated CHICKEN release This is a manual page for an old and unsupported version of CHICKEN. If you are still using it, please consider migrating to the latest version. You can find the manual for the latest release [[/manual|here]]. [[tags: manual]] [[toc:]] == Locations It is also possible to define variables containing unboxed C data, so called ''locations''. It should be noted that locations may only contain simple data, that is: everything that fits into a machine word, and double-precision floating point values. === define-location <macro>(define-location NAME TYPE [INIT])</macro> Identical to {{(define-external NAME TYPE [INIT])}}, but the variable is not accessible from outside of the current compilation unit (it is declared {{static}}). === let-location <macro>(let-location ((NAME TYPE [INIT]) ...) BODY ...)</macro> Defines a lexically bound location. === location <macro>(location NAME)</macro><br> <macro>(location X)</macro> <read>#$</read> This form returns a pointer object that contains the address of the variable {{NAME}}. If the argument to {{location}} is not a location defined by {{define-location}}, {{define-external}} or {{let-location}}, then (location X) is essentially equivalent to (make-locative X) (See the [[Unit lolevel#locatives|manual section on locatives]] for more information about locatives) Note that {{(location X)}} may be abbreviated as {{#$X}}. <enscript highlight=scheme> (define-external foo int) ((foreign-lambda* void (((c-pointer int) ip)) "*ip = 123;") (location foo)) foo ==> 123 </enscript> This facility is especially useful in situations, where a C function returns more than one result value: <enscript highlight=scheme> #> #include <math.h> <# (define modf (foreign-lambda double "modf" double (c-pointer double)) ) (let-location ([i double]) (let ([f (modf 1.99 (location i))]) (print "i=" i ", f=" f) ) ) </enscript> See [[/location-and-c-string-star|location and c-string*]] for a tip on returning a {{c-string*}} type. {{location}} returns a value of type {{c-pointer}}, when given the name of a callback-procedure defined with {{define-external}}. --- Previous: [[Callbacks]] Next: [[Other support procedures]] Description of your changes:

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