On Fri, Mar 18, 2011 at 5:58 PM, Matthew Mondor <mm_li...@pulsar-zone.net>wrote:
> Hello, > > When looking at the HyperSpec on those functions, it seems undefined > what happens when a supplied index is not a "valid array index", thus, > from 0 below the array size. The exception is ELT, which should signal > a condition of type TYPE-ERROR. > > In practice however, it seems that implementations attempt to signal an > error condition for invalid index access. > > In SBCL, AREF, SVREF, CHAR, SCHAR will signal a uniform condition of > type SB-INT:INVALID-ARRAY-INDEX-ERROR: > Which version is this? I get this one with the latest update from Fink (handler-case (let ((a (make-array '(2 3)))) (aref a 2 1)) (error (c) (print c))) => #<TYPE-ERROR expected-type: BIT datum: 2> > Index 4 out of bounds for <insert array type here>, > should be nonnegative and <<insert size here>. > > Although a different behaviour for ELT: > The index 4 is too large. [SB-KERNEL:INDEX-TOO-LARGE-ERROR] > > > For ECL, the condition type and error message varies, and SVREF even > behaves differently than the others: > > CHAR, SCHAR: [SIMPLE-ERROR] > AREF: [SIMPLE-TYPE-ERROR] > SVREF: (this differs in interpreted and compiled mode) > Interpreted mode: In function SVREF, the index into the object 4. takes a > value #(1 2 3) out of the range (INTEGER 0 2). [SIMPLE-TYPE-ERROR] > Compiled mode: Returns the supplied vector instead of signaling an error. > ELT: [SIMPLE-TYPE-ERROR] > I have changed this. CHAR, SCHAR, SVREF and ELT now use the same error reporting function. I also fixed a typo in AREF. SVREF in compiled mode, though, may be directly translated into a vector access, if optimization levels are large enough. In this case no error checking is performed and the value you may get is completely random, as Pascal explained. Compare > (funcall (compile 'nil '(lambda (x) (svref x 3))) #(1 2 3)) [...] Condition of type: SIMPLE-TYPE-ERROR In function AREF, the index into the object #(1 2 3). takes a value 3 out of the range (INTEGER 0 2). [...] > (funcall (compile 'nil '(lambda (x) (declare (optimize (safety 0))) (svref x 3))) #(1 2 3)) [...] Condition of type: SEGMENTATION-VIOLATION Detected access to an invalid or protected memory address. Available restarts: Juanjo -- Instituto de Física Fundamental, CSIC c/ Serrano, 113b, Madrid 28006 (Spain) http://juanjose.garciaripoll.googlepages.com
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