c++ - (!file) 和 (!file.is_open()) 有什么区别？

Question

if(!file) 和 if(!file.is_open()) 有什么区别？我用它们来检查文件是否已成功打开/读取。

#include<iostream>
#include<fstream>
using namespace std;

int main(){
ifstream file;

// first one
if (!file) 
   cout<<"File is not opened"<<endl;
else 
   . . .

//second one
if (!file.is_open()) 
   cout<<"File is not opened"<<endl;
else 
   . . .
}

Answer 1

c++ 文档解释了 operator!

Returns true if an error has occurred on the associated stream. Specifically, returns true if badbit or failbit is set in rdstate()

另一方面，is_open()

Checks if the file stream has an associated file. Returns true if the file stream has an associated file, false otherwise

如果您想知道文件是否成功打开，请使用is_open()。它也更能表达您的意图。