Shift the bits of this bitset left (towards the most significant bit) by the specified pos and return a reference to this modifiable bitset. For all bits with position I where I <= pos, the new value is 0. The behavior is undefined unless pos <= N.
pos
I <= pos
pos <= N
Declared in <bslstl_bitset.h>
<bslstl_bitset.h>
bitset<N>& operator<<=(std::size_t pos) noexcept;