问题描述
预期的节目输出：
键是：0字符串是：你好
键是：1字符串是：再见
键是：2字符串是：结束
实际输出：
键是：0字符串是：结束
键是： 1字符串是：
键是：2字符串是：
我做错了什么？
如果我每次都声明我的参考新鲜，比如把{}放在我插入的
个地方并做
std :: string& MyString =（* it）.second;
每次出来都正确。
为什么我不能重复使用这些参考文件？
花了很长时间才发现我的程序中导致这种情况的原因。这个
只是一个显示问题的测试程序。
#include< iostream>
#include< string>
#include< map>
std :: map< unsigned int，std :: string> MyMap;
int main（）
{
unsigned int ID = 0;
std ::地图< unsigned int，std :: string> :: iterator it = MyMap.insert（
MyMap.end（），std :: make_pair< unsigned int，std :: string>（ID，
std :: string（）））;
std :: string& MyString =（* it）.second;
MyString =" Hello";
ID = 1;
it = MyMap.insert（MyMap.end（），std :: make_pair< unsigned int，
std :: string>（ID，std :: string（）））;
std :: string& MyString2 =（* it）.second;
MyString =" Goodbye";
ID = 2;
it = MyMap.insert（MyMap.end（），std :: make_pair< unsigned int，
std :: string>（ID，std :: string（）））;
MyString =（* it）.second;
MyString =" The End";
for（std :: map< unsigned int，std :: string> :: iterator i = MyMap.begin（）;
i！= MyMap.end（）; ++ i）
{
std :: cout<< 关键是： << （* i）.first<< "字符串是： <<
（* i）.second<< std :: endl;
}
std :: string wait;
std :: cin>>等待;
}
Expected output of program:
Key is: 0 String is: Hello
Key is: 1 String is: Goodbye
Key is: 2 String is: The end
Actual output:
Key is: 0 String is: The End
Key is: 1 String is:
Key is: 2 String is:
What am I doing wrong?
If I declare my reference fresh each time, such as putting { } around the
places I insert and doing
std::string& MyString = (*it).second;
each time it will come out right.
Why can''t I reuse the references?
It took a long time to find out what was causing this in my program. This
is just a test program showing the issue.
#include <iostream>
#include <string>
#include <map>
std::map<unsigned int, std::string> MyMap;
int main ()
{
unsigned int ID = 0;
std::map< unsigned int, std::string>::iterator it = MyMap.insert(
MyMap.end(), std::make_pair< unsigned int, std::string >( ID,
std::string() ) );
std::string& MyString = (*it).second;
MyString = "Hello";
ID = 1;
it = MyMap.insert( MyMap.end(), std::make_pair< unsigned int,
std::string >( ID, std::string() ) );
std::string& MyString2 = (*it).second;
MyString = "Goodbye";
ID = 2;
it = MyMap.insert( MyMap.end(), std::make_pair< unsigned int,
std::string >( ID, std::string() ) );
MyString = (*it).second;
MyString = "The End";
for ( std::map< unsigned int, std::string >::iterator i = MyMap.begin();
i != MyMap.end(); ++i )
{
std::cout << "Key is: " << (*i).first << " String is: " <<
(*i).second << std::endl;
}
std::string wait;
std::cin >> wait;
}
推荐答案
This doesn''t initialize a reference, it assigns the value of second
into where MyString was initialized (your first insertion).
哦好吧，拍摄。你是对的。那完全超越了我。如果在同一行声明了引用
，那么它会初始化它。
嗯...那么如何分配已经初始化的引用？
IE
int int1;
int int2;
int& MyRef = int1;
我该怎么做才能让MyRef现在指向int2？或者我可以吗？
Oh, well, shoot. You''re right. That totally excaped me. If the reference
is declared on the same line, then it initializes it.
Hmm.. so how do you assign a reference that has already been initialized?
I.E.
int int1;
int int2;
int& MyRef = int1;
Who do I do to get MyRef to point to int2 now? Or can I?
这会做另一个这样的任务
And this does another such assignment
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