您的 isNewline 函数没有问题。

问题是如何将字符串传递给 isNewline 函数。

The problem is how you get the string to be passed to isNewline function.

我怀疑您使用了类似 getline（fin，aLine）之类的字符串来获取如下字符串？

I suspect you use something like getline(fin,aLine) to get the string like below?

while(getline(fin,aLine)){
   cout<<aLine<<endl; //aLine will never contain newline character because getline never save it
   cout<<isNewline(aLine)<<endl; // so this will never output "(newline)"
}

getline 不会将换行符保存到 aLine

getline does not save the newline character into aLine