c - What aspects of signed left shift are undefined with GCC? -

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basically asking translation of:

gcc not use latitude given in c99 treat aspects of signed `<<' undefined, subject change.

(gcc 4.8.1 manual, paragraph 4.5)

what 'latitude' given? aspects?

other answers have pointed out aspects of << undefined behavior. guess want "translation" of gcc common language.

if behavior undefined c standard, compiler implementors can take "latitude" suits them if such case occurs. in particular, don't have implement diagnostic or detection of case, , may pretend never happens. responsability of programmer write program such behavior defined.

in case of left shift, means compiler not have check overflow , can pretend loop like

for (int = 1; > 0; <<= a) {  .... change in complicated way ... }

would never terminate.

the sentence citing indicates don't such thing, yet, future versions of gcc might so.


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