##實戰c++中的vector系列--構造、operator=和assign區別 vector也許是實際過程中使用最多的stl容器，看似簡單，其實有很多技巧和陷阱。 著重看一看vector的構造，暫時按照C++11： ~~~ default (1) explicit vector (const allocator_type& alloc = allocator_type()); fill (2) explicit vector (size_type n); vector (size_type n, const value_type& val, const allocator_type& alloc = allocator_type()); range (3) template <class InputIterator> vector (InputIterator first, InputIterator last, const allocator_type& alloc = allocator_type()); copy (4) vector (const vector& x); vector (const vector& x, const allocator_type& alloc); move (5) vector (vector&& x); vector (vector&& x, const allocator_type& alloc); initializer list (6) vector (initializer_list<value_type> il, const allocator_type& alloc = allocator_type()); ~~~ 直接看看下面的代碼，就知道如何構造一個vector了： ~~~ #include <iostream> #include <vector> int main () { std::vector<int> first; // default (1) std::vector<int> second (4,100); // fill (2) std::vector<int> third (second.begin(),second.end()); // range (3) std::vector<int> fourth (third); // a copy of third // the iterator constructor can also be used to construct from arrays: int myints[] = {16,2,77,29}; std::vector<int> fifth (myints, myints + sizeof(myints) / sizeof(int) ); std::cout << "The contents of fifth are:"; for (std::vector<int>::iterator it = fifth.begin(); it != fifth.end(); ++it) std::cout << ' ' << *it; std::cout << '\n'; return 0; } ~~~ ===========================================================? vector重載了=運算符，也有一個叫assign的方法，而且有什么區別嗎？ **std::vector::operator=**? 直接代碼： ~~~ #include <iostream> #include <vector> int main () { std::vector<int> foo (3,0); std::vector<int> bar (5,0); bar = foo; foo = std::vector<int>(); std::cout << "Size of foo: " << int(foo.size()) << '\n'; std::cout << "Size of bar: " << int(bar.size()) << '\n'; return 0; } //結果： Size of foo: 0 Size of bar: 3 ~~~ 這里需要說明的是：? replacing its current contents? modifying its size accordingly **std::vector::assign**? 同樣直接代碼： ~~~ #include <iostream> #include <vector> int main () { std::vector<int> first; std::vector<int> second; std::vector<int> third; first.assign (7,100); // 7 ints with a value of 100 std::vector<int>::iterator it; it=first.begin()+1; second.assign (it,first.end()-1); // the 5 central values of first int myints[] = {1776,7,4}; third.assign (myints,myints+3); // assigning from array. std::cout << "Size of first: " << int (first.size()) << '\n'; std::cout << "Size of second: " << int (second.size()) << '\n'; std::cout << "Size of third: " << int (third.size()) << '\n'; return 0; } //輸出： Size of first: 7 Size of second: 5 Size of third: 3 ~~~ 這里同樣需要說明：? replacing its current contents? modifying its size accordingly