How to Gracefully Handle Different Line Endings in C 's `std::getline`?

Gracefully Handling Different Line Endings in std::istream::getline

When reading text files, encountering varying line endings such as 'n', 'r', and 'rn' can pose challenges. std::getline is a convenient function for retrieving lines from an input stream, but it may leave residual 'r' characters at the end of the string.

As pointed out by Neil, the C runtime is generally equipped to handle line ending conventions based on the platform. However, interoperability between different systems requires a more robust approach.

Here's a customized function that seamlessly processes all three line ending types:

std::istream& safeGetline(std::istream& is, std::string& t)
{
    t.clear();

    std::istream::sentry se(is, true);
    std::streambuf* sb = is.rdbuf();

    for(;;) {
        int c = sb->sbumpc();
        switch (c) {
        case '\n':
            return is;
        case '\r':
            if(sb->sgetc() == '\n')
                sb->sbumpc();
            return is;
        case std::streambuf::traits_type::eof():
            if(t.empty())
                is.setstate(std::ios::eofbit);
            return is;
        default:
            t += (char)c;
        }
    }
}

In this function, we utilize a streambuf object to read characters one by one efficiently. Each character is examined, and based on its type, appropriate actions are taken to handle line endings.

A sample test program illustrates the usage of safeGetline:

int main()
{
    std::string path = ... // Insert path to test file here

    std::ifstream ifs(path.c_str());
    if(!ifs) {
        std::cout << "Failed to open the file." << std::endl;
        return EXIT_FAILURE;
    }

    int n = 0;
    std::string t;
    while(!safeGetline(ifs, t).eof())
        ++n;
    std::cout << "The file contains " << n << " lines." << std::endl;
    return EXIT_SUCCESS;
}

By employing this approach, you can confidently read text files from various origins, ensuring graceful handling of different line endings.

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