检查文件是否已成功使用ifstream打开 [英] Checking if a file opened successfully with ifstream

问题描述

我有以下将打开一个文件进行阅读。但是，我想检查以确保文件已成功打开，所以我使用失败，看看是否已设置标志。但是，我仍然得到以下错误：

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的新用户，因为我来自C.所以不知道我理解这个错误：

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

无法调用成员函数bool std :: basic_ios <_CharT，
_Traits> :: fail（）const [with _CharT = char，_Traits = std :: char_traits]'without object

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

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，必须在实例不是类型，所以如果你想使用fail（），用 input_stream.fail（）替换！input_stream 我的代码在上面。

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.

我不得不想知道你想在这里实现。您正在打开该文件并立即关闭它。你只是试图检查文件是否存在？

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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