getline()的实际行为如何? [英] How does getline() actually behave?
问题描述
我有2个问题:
-
如果while循环结束后再次执行"getline(in，line)"，则s会发生什么?
What happens to s if I again do a "getline(in,line)" after the while loop ends?
ifstream in("string.txt");
string s, line;
s = "";
while(getline(in,line))
{
s = s + line + "\n";
}
cout<<s<<endl<<"******************************************"<<endl;
getline()函数:每次调用它时，它是否都进入上述代码中ifstream"in"对象的"next"行?如果是这样，当while循环结束并且我再次调用同一个函数时会发生什么?(与第一个问题几乎相同，只是有细微的差别)
The getline() function: everytime it is called, does it goes to the "next" line of the ifstream "in" object in the above code? If so what happens when the while loop ends and I call the same function again? (almost the same as first question, just a subtle difference)
推荐答案
如果while循环结束后再次执行"getline(in，line)"，那么s会发生什么?
What happens to s if I again do a "getline(in,line)" after the while loop ends?
当 std :: getline()返回类似于布尔值 false 的内容时，循环结束.当您查看函数的签名时，您会看到它返回流.流有隐式转换为类似于其状态的类似布尔的形式.如果 if(stream)将流评估为 false ，则意味着该流处于不良状态.这可以是EOF标志集，也可以是错误标志之一，或者两者都可以.
任何使用处于不良状态的流的尝试都将失败.什么都不会读.
The loop ends when std::getline() returns something that resembles a boolean false. When you look at the signature of the function you will see that it returns the stream. Streams have an implicit conversion to something boolean-like that resembles their state. If if(stream) evaluates the stream to false, then that means that the stream is in a bad state. This could be the EOF flag set or one of the error flags, or both.
Any attempt to use a stream that is in a bad state will fail. Nothing will be read.
getline()函数:每次调用它时，它是否都进入上述代码中ifstream"in"对象的"next"行?如果是这样，当while循环结束并且我再次调用同一个函数时会发生什么?(与第一个问题几乎相同，只是细微的差别)
The getline() function: everytime it is called, does it goes to the "next" line of the ifstream "in" object in the above code? If so what happens when the while loop ends and I call the same function again? (almost the same as first question, just a subtle difference)
这与 std :: getline()没有关系.打开的文件中的位置是(文件)流的属性.每次(重新)打开文件进行读取(不传递用于设置位置的额外参数)时，该位置都将设置为流(文件)的开头.
This has nothing to do with std::getline(). The position in the opened file is a property of the (file) stream. Every time you (re-)open the file for reading (without passing extra parameter for setting the position), the position is set to the beginning of the stream (file).
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