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pure |
Many functions have no effects except the return value and their
return value depends only on the parameters and/or global variables.
Such a function can be subject
to common subexpression elimination and loop optimization just as an
arithmetic operator would be. These functions should be declared
with the attribute pure. For example,
int square (int) __attribute__ ((pure));
says that the hypothetical function square is safe to call
fewer times than the program says.
Some common examples of pure functions are strlen or memcmp.
Interesting non-pure functions are functions with infinite loops or those
depending on volatile memory or other system resource, that may change between
two consecutive calls.
See also: const