C++ 使用打开的文件流创建类

我创建了一个类，该类应该读取DNA序列：它包含一个if流私有成员：

接口：

class Sequence_stream {
    const char* FileName;
    std::ifstream FileStream;
    std::string FileFormat;

public:
    Sequence_stream(const char* Filename, std::string Format);
    NucleotideSequence get();
};

实施：

Sequence_stream::Sequence_stream(const char* Filename, std::string Format)
{
    FileName = Filename;
    FileStream.open(FileName);
    FileFormat = Format;
    std::cout << "Filestream is open: " << FileStream.is_open() << std::endl;
}

NucleotideSequence Sequence_stream::get()
{
    if (FileStream.is_open())
    {
        char currentchar;
        int basepos = 0;
        std::string name;
        std::vector<Nucleotide> sequence;
        currentchar = FileStream.get();
        if (currentchar == '>' && false == FileStream.eof()) {  // Check that the start of the first line is the fasta head character.
            currentchar = FileStream.get(); // Proceed to get the full name of the sequence. Get characters until the newline character.
            while(currentchar != '\n' && false == FileStream.eof())
            {
                if (true == FileStream.eof()) {
                    std::cout << "The file ends before we have even finished reading in the name. Returning an empty NucleotideSequence" << std::endl;
                    return NucleotideSequence();
                }
                name.append(1, currentchar);
                currentchar = FileStream.get();
            } // done getting names, now let's get the sequence.
            currentchar = FileStream.get();
            while(currentchar != '>' && false == FileStream.eof())
            {
                if(currentchar != '\n'){
                    basepos++;
                    sequence.push_back(Nucleotide(currentchar, basepos));
                }
                currentchar = FileStream.get();
            }
            if(currentchar == '>')
            {
                FileStream.unget();
            }
            return NucleotideSequence(name, sequence);
        } else {
            std::cout << "The first line of the file was not a fasta format description line beginning with '>'. Are you sure the file is of FASTA format?" << std::endl;
            return NucleotideSequence();
        }

    } else {
        std::cout << "The filestream is not open..." << std::endl;
        return NucleotideSequence();
    }
}

虽然我认为构造函数会打开if流。当对象被创建并包含一个开放流时，我需要做什么来纠正这一点？（我知道我还没有包括一个析构函数，它将在销毁对象时关闭流）

谢谢，

---

Ben.

您的示例显示，is\u open返回false。我认为您应该在构造函数中检查文件是否确实已打开，如果未打开，则抛出

---

在您的情况下，我怀疑这是由于将“~/Dropbox/1_20dd5.fasta”作为输入参数传递所致。您是否使用完整路径名进行测试，没有~？我不知道处理真实路径扩展的C++库（比如Python的操作系统.PATH）。如果你尝试在构造函数之外打开流，那会怎么样？比如：MyDNAStream.FileStream.open（“filename”）在main（）中？这行吗？代码没有太大问题，文件由于其他原因无法打开。顺便说一句，关闭流不需要编写析构函数。这将自动发生，因为ifstream析构函数将为您关闭流（令人惊讶的是，有多少新手没有意识到这一点）。是的

~

由shell处理，这里没有shell，所以

~

的解释不正确。我发现问题确实是路径和~：如果我也将输入文件粘贴在桌面上，只需指定文件名，它就可以工作了。Howe最好为构造函数实现一个try-catch-函数在catch之后不会结束并返回一个带有关闭的if流成员的对象吗？当发生意外情况时，应该抛出w std:：exception，调用构造函数时在main中捕获它，如：

code

try{Sequence_stream MyDNAStream（“~/Dropbox/120dd5.fasta”，“fasta”）；}{catch（std:：exception&e）{//do something}如果您不捕获，那么您的程序将直接进入内核。或者，如果您不想使用异常，则必须在类中实现一个方法来检查您创建的对象的完整性（类似于is_open（）方法）。

int main()
{
    std::cout << "Let's try and read in a sequence!" << std::endl;
    std::cout << "First we'll create a stream!" << std::endl;
    Sequence_stream MyDNAStream("~/Dropbox/1_20dd5.fasta", "fasta");
    std::cout << "Done!" << std::endl;
    std::cout << "Now let's try and get a sequence!" << endl;
    NucleotideSequence firstsequence = MyDNAStream.get();
    return 0;
} 

Let's try and read in a sequence!
First we'll create a stream!
Filestream is open: 0
Done!
The filestream is not open...
logout

[Process completed]