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顺序容器访问成员函数返回的是引用即front、back、下标和at 返回的是引用这里以front成员函数为例，找到front的源码 /** * Returns a read/write reference to the data at the first * element of the %vector. */ reference front() _GLIBCXX_NOEXCEPT { return *begin();

直接上源码template<typename _BidirectionalIterator, typename _Compare> bool __next_permutation(_BidirectionalIterator __first, _BidirectionalIterator __last, _Compare __comp) { if (__first == __last) //没有元素，return false re