C++ list iterator arithmetic

Question

I am aware that you cannot use iterators with list in the form "it +n" but why is that when I use ++it the program is able to compile ie:

//program compiles
list<int> v {1,2,3,4}; 
auto begin = v.begin(),
end = v.end(); 
while (begin != end) {
    ++begin;  
    begin = v.insert(begin, 42); 
    ++begin;  // advance begin past the element we just added
}

//program doesn't compile
list<int> v{1,2,3,4}; 
auto begin = v.begin(),
end = v.end(); 
while (begin != end) {
    begin+=1; //or alternatively begin = begin +1 
    begin = v.insert(begin, 42);  // insert the new value
    ++begin;  // advance begin past the element we just added
}

Answer 1

根据standart std :: list实现的双向迭代器http://www.cplusplus.com/reference/iterator/BidirectionalIterator/没有“ + =”运算符