STL vector中的operator=方法（30）

原文地址:http://www.cplusplus.com/reference/algorithm/unique/

public member function

<vector>

std::vector::operator=

• C++98
• C++11

copy (1)move (2)initializer list (3)

vector& operator= (const vector& x);

vector& operator= (vector&& x);

vector& operator= (initializer_list<value_type> il);

Assign content

Assigns new contents to the container, replacing its current contents, and modifying itssizeaccordingly.调整当前容器内容，替换当前内容，并调整当前容器的大小。

• 
  
  
• C++11

Thecopy assignment(1) copies all the elements fromxinto the container (withxpreserving its contents).
从x中依次复制其元素到该vector中，x中的元素依旧有效。

Themove assignment(2) moves the elements ofxinto the container (xis left in an unspecified but valid state).
从x中移动其元素到该vector中，(x依旧有效但不指定是否离开？)

Theinitializer list assignment(3) copies the elements ofilinto the container.
从初始化列表中复制元素到容器中。

The container preserves itscurrent allocator, except if theallocator traitsindicate thatx's allocator shouldpropagate. Thisallocatoris used (through itstraits) toallocateanddeallocatestorage if a reallocation happens, and toconstructordestroyelements, if needed.
容器保持现有的内存分配器，除非分配器的特性指明了应该继承x的内存分配器，那么将使用其内存分配器去分配及释放内存，如果发生重分配，或者构造，析构需要的时候，就使用该分配器。

相应例子及结果截图:

（1）

#include <iostream>
#include <vector>
#include <algorithm>
using namespace std;
int main()
{
	vector<int> v1={1,2,3,4};
	vector<int> v2={11,12,13,14};
	cout<<"v1=";
	for_each(v1.begin(),v1.end(),[](const int &m){cout<<m<<" ";});
	cout<<endl;
	cout<<"v2=";
	for_each(v2.begin(),v2.end(),[](const int &m){cout<<m<<" ";});
	cout<<endl;
	v1=v2;
	cout<<"after v1=v2:"<<endl;
	cout<<"v1=";
	for_each(v1.begin(),v1.end(),[](const int &m){cout<<m<<" ";});
	cout<<endl;
	cout<<"v2=";
	for_each(v2.begin(),v2.end(),[](const int &m){cout<<m<<" ";});
	cout<<endl;


}

截图：

(2)

#include <iostream>
#include <vector>
#include <algorithm>
#include <initializer_list>
using namespace std;

vector<int> returnVector(){
	vector<int> v2={88,99,111};
	cout<<"v2.data="<<v2.data()<<endl;
	return v2;
}

int main()
{
	vector<int> v1={1,2,3,4};
	cout<<"v1=";
	for_each(v1.begin(),v1.end(),[](const int &m){cout<<m<<" ";});
	cout<<endl;	
	cout<<"v1.data="<<v1.data()<<endl;
	v1=returnVector();
	cout<<"after v1=returnVector():"<<endl;
	cout<<"v1=";
	for_each(v1.begin(),v1.end(),[](const int &m){cout<<m<<" ";});
	cout<<endl;
	cout<<"v1.data="<<v1.data()<<endl;
	


}

运行截图:

(3)

#include <iostream>
#include <vector>
#include <algorithm>
#include <initializer_list>
using namespace std;
int main()
{
	vector<int> v1={1,2,3,4};
	cout<<"v1=";
	for_each(v1.begin(),v1.end(),[](const int &m){cout<<m<<" ";});
	cout<<endl;	
	v1={999,888,777,666};
	cout<<"after v1={999,888,777,666}:"<<endl;
	cout<<"v1=";
	for_each(v1.begin(),v1.end(),[](const int &m){cout<<m<<" ";});
	cout<<endl;
	


}

结果截图:

Any elements held in the container before the call are eitherassigned toordestroyed.

使用该函数之前其元素依旧存储。（？？）

Parameters

x

Avectorobject of the same type (i.e., with the same template parameters,TandAlloc).

一个和该vector相同类型（模版参数T和Alloc）的vector

il

Aninitializer_listobject. The compiler will automatically construct such objects frominitializer listdeclarators.

一个初始化列表对象，编译器将自动从该对象中构造元素。
Member typevalue_typeis the type of the elements in the container, defined invectoras an alias of its first template parameter (T).

Return value

*this

Example

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16

// vector assignment #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; }

Edit & Run

Output:

Size of foo: 0
Size of bar: 3

Complexity

Linear insize.
和大小线性相关。

Iterator validity

All iterators, references and pointers related to this container before the call are invalidated.所以的迭代器，指针已经引用都将失效。

In themove assignment, iterators, pointers and references referring to elements inxare also invalidated.
在move assignment这种情况下，指向x的指针，迭代器，引用也将失效。

Data races

All copied elements are accessed.复制的元素将被访问。
Themove assignment (2)modifiesx.在move assignment (2)中x将被修改.
The container and all its elements are modified.
容器及所有元素都将被修改。

Exception safety

Basic guarantee:if an exception is thrown, the container is in a valid state.如果抛出异常，容器依旧有效。
Ifallocator_traits::constructis not supported with the appropriate arguments for the element constructions, or ifvalue_typeis notcopy assignable(ormove assignablefor(2)), it causesundefined behavior.
如果内存分配器不支持元素的构造，或者值类型不支持复制赋值或者移动赋值（在(2)这种情况下）,会导致为定义的行为。

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2014-8-19

于GDUT