问题描述

我有以下内容可以打开文件进行阅读.但是，我想检查以确保文件已成功打开，因此我使用失败来查看标志是否已设置.但是，我不断收到以下错误:

I have the following that will open a file for reading. However, I want to check to make sure that the file was open successfully, so I am using the fail to see if the flags have been set. However, I keep getting the following error:

我是 C++ 新手，因为我来自 C.所以不确定我是否理解这个错误:

I am new to C++, as I am coming from C. So not sure I understand this error:

不能调用成员函数‘bool std::basic_ios<_CharT，_Traits>::fail() const [with _CharT = char, _Traits = std::char_traits]' 无对象

cannot call member function ‘bool std::basic_ios<_CharT, _Traits>::fail() const [with _CharT = char, _Traits = std::char_traits]’ without object

代码:

int devices::open_file(std::string _file_name)
{
    ifstream input_stream;

    input_stream.open(_file_name.c_str(), ios::in);

    if(ios::fail() == true) {
        return -1;
    }

    file_name = _file_name;

    return 0;
}

推荐答案

你可以简单地这样做:

int devices::open_file(std::string _file_name)
{
    ifstream input_stream;    
    input_stream.open(_file_name.c_str(), ios::in);
    if(!input_stream)
    {
        return -1;
    } 
    file_name = _file_name;
    return 0;
}

fail() 不是静态方法，你必须在一个实例上而不是一个类型上调用它，所以如果你想使用fail()，请将 !input_stream 替换为 input_stream.fail() 在我上面的代码中.

fail() is not a static method, you must call it on an instance not a type, so if you want to use fail(), replace !input_stream with input_stream.fail() in my code above.

我确实想知道你在这里想达到什么目的.您正在打开文件并立即再次关闭它.你只是想检查文件是否存在?

I do have to wonder what you're trying to achieve here. You're opening the file and immediately close it again. Are you simply trying to check if the file exists?

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