It’s all in your things.size()
type. It isn’t int
, but size_t
(it exists in C++, not in C) which equals to some “usual” unsigned type, i.e. unsigned int
for x86_32.
Operator “less” (<) cannot be applied to two operands of different sign. There’s just no such opcodes, and standard doesn’t specify, whether compiler can make implicit sign conversion. So it just treats signed number as unsigned and emits that warning.
It would be correct to write it like
for (size_t i = 0; i < things.size(); ++i) { /**/ }
or even faster
for (size_t i = 0, ilen = things.size(); i < ilen; ++i) { /**/ }