如何从C ++中的文本文件中读取长行？

Question

I am using the following code for reading lines from a text-file. What is the best method for handling the case where the line is greater than the limit SIZE_MAX_LINE?

void TextFileReader::read(string inFilename)
{
    ifstream xInFile(inFilename.c_str());
    if(!xInFile){
        return;
    }

    char acLine[SIZE_MAX_LINE + 1];

    while(xInFile){
        xInFile.getline(acLine, SIZE_MAX_LINE);
        if(xInFile){
            m_sStream.append(acLine); //Appending read line to string
        }
    }

    xInFile.close();
}

Answer 1

Don't use istream::getline() . It deals with naked character buffers and is therefor prone to errors. Better use std::getline(std::istream&,std::string&, char='\\n') from the <string> header:

std::string line;

while(std::getline(xInFile, line)) {
    m_sStream.append(line);
    m_sStream.append('\n'); // getline() consumes '\n'
}

Answer 2

Since you're using C++ and iostream already, why not use std::string 's getline function ?

std::string acLine;
while(xInFile){
    std::getline(xInFile, acLine);
    // etc.
}

---

And, use xInFile.good() to ensure eofbit and badbit and failbit are not set.

Answer 3

If you use the free function in string, you don't have to pass a max length. It also the uses C++ string type.