使用stringstream>>if语句中的运算符 [英] using stringstream >> operator in if statement

问题描述

以下代码段旨在尝试使用stringstream对象从字符串中提取整数，并检测整数提取是否成功.stringstream类继承>>运算符，以返回对istream实例的引用.失败的整数提取如何导致myStream的str成员仍为strInput时等于0?

The following code snippet is meant to try and extract an integer from a string using a stringstream object and detect whether integer extraction was successful or not. The stringstream class inherits the >> operator to return a reference to an istream instance. How does failed integer extraction lead to myStream being equal to 0 while its str member is still strInput?

stringstream myStream(strInput);
if (myStream >> num){//successfull integer extraction}
else{//unsuccessfull integer extraction
cout<<myStream<<endl;
cout<<myStream.str().c_str()<<endl;}

推荐答案

stream ，它会返回(类似)！fail()-或在 void * 失败时返回NULL的情况.因此，如果流没有失败，那就很好. operator>> 返回对 stream 对象的引用，因此编译器说嗯，不能将流对象与真值进行比较，让我们看看是否可以用它做一个 bool 或 void * ，是的，我们可以使用它.

There is an operator bool() or operator void*() for stream, which returns (something like) !fail() - or in case of void * a NULL when it failed. So, if the stream hasn't failed, it's fine. The operator >> returns a reference to the stream object, so the compiler says "Hmm, can't compare a stream object to truth, let's see if we can make a bool, or void * from it, yes we can, so let's use that.

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