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C++11之后，bitset的构造函数新加了两种形式：
bitset<bits>::bitset (const string& str, string::size_type str_idx, string::size_type str_num, string::charT zero) bitset<bits>::bitset (const string& str, string::size_type str_idx, string::size_type str_num, string::charT zero, string::charT one)
在vs2015中作如下实现：
template<class _Elem, class _Tr, class _Alloc> explicit bitset(const basic_string<_Elem, _Tr, _Alloc>& _Str, _BITSET_SIZE_TYPE _Pos = 0, _BITSET_SIZE_TYPE _Count = basic_string<_Elem, _Tr, _Alloc>::npos, _Elem _E0 = (_Elem)‘0‘, _Elem _E1 = (_Elem)‘1‘) { // construct from [_Pos, _Pos + _Count) elements in string _Construct(_Str, _Pos, _Count, _E0, _E1); }
其_Construct如下：
template<class _Elem, class _Tr, class _Alloc> void _Construct( const basic_string<_Elem, _Tr, _Alloc>& _Str, _BITSET_SIZE_TYPE _Pos, _BITSET_SIZE_TYPE _Count, _Elem _E0, _Elem _E1) { // initialize from [_Pos, _Pos + _Count) elements in string if (_Str.size() < _Pos) _Xran(); // _Pos off end if (_Str.size() - _Pos < _Count) _Count = _Str.size() - _Pos; // trim _Count to size typename basic_string<_Elem, _Tr, _Alloc>::size_type _Num; for (_Num = 0; _Num < _Count; ++_Num) if (!_Tr::eq(_Str[_Pos + _Num], _E0) && !_Tr::eq(_Str[_Pos + _Num], _E1)) _Xinv(); if (_Bits < _Count) _Count = _Bits; // trim _Count to length of bitset _Tidy(); for (_Pos += _Count, _Num = 0; _Num < _Count; ++_Num) if (_Tr::eq(_Str[--_Pos], _E1)) set(_Num); }
在Nicolai M Josuttis的标准库参考书中有这么一句话：Throw invalid_argument if one of the characters is neither ’0’/zero nor ’1’/one.但在vs2015中却可以以’1’/zero和’0’/one的组合作为参数。程序会用0和1分别代替1和0应填充的位置，不足位仍用0填充。不会抛出异常。同时我没在标准文档中找到相关说明。只在草案n4567中找到这么一句：
The function then throws invalid_argument if any of the rlen characters in str beginning at position
pos is other than zero or one. The function uses traits::eq() to compare the character values.
显然这并没太大关系。
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原文地址：http://www.cnblogs.com/ptolemaeus/p/BitSet_Construct.html
