C++ check end of line

Question

I got a problem in C++ where I need to parse a file with multiple lines (random strings with random length) and transform the uppercase characters in lowercase character and store the lines in a vector of strings. I'm trying to parse the file character by character but don't know how to identify the end of a line.

Answer 1

If you really want to parse a line character for character, then you have a lot of work. And, you depend a little bit on your environment. Lines could be terminated with '\n' or '\r' or "\r\n".

I would really recommend to use a function that has been designed to get a complete line. And this function is std::getline. If your line would not contain white spaces, you could also read a string directly with the extractor operator like this: std::string s; ifstreamVariable >> s;

To be independent of such behavior, we can implement a proxy class to read complete lines and put this into a std::string.

The file can be read into a vector, with the proxy class and the range based vector constructor.

For transforming to lowercase, we will use std::transform. That is very simple.

Please see the following example code.

#include <iostream>
#include <vector>
#include <algorithm>
#include <iterator>
#include <sstream>

std::istringstream testDataFile(
R"#(Line 0 Random legth asdasdasfd
Line 1 Random legth asdasdasfd sdfgsdfgs sdfg
Line 2 Random legth asdasdasfd sdfgs sdfg
Line 3 Random legth a sddfgsdfgs sdfg
Line 4 Random legth as sds sg
)#");


class CompleteLine {    // Proxy for the input Iterator
public:
    // Overload extractor. Read a complete line
    friend std::istream& operator>>(std::istream& is, CompleteLine& cl) { std::getline(is, cl.completeLine); return is; }
    // Cast the type 'CompleteLine' to std::string
    operator std::string() const { return completeLine; }
protected:
    // Temporary to hold the read string
    std::string completeLine{};
};

int main()
{
    // Read complete source file into maze, by simply defining the variable and using the range constructor
    std::vector<std::string> strings{ std::istream_iterator<CompleteLine>(testDataFile), std::istream_iterator<CompleteLine>() };

    // Convert all strings in vector ro lowercase
    std::for_each(strings.begin(), strings.end(), [](std::string& s) { std::transform(s.begin(), s.end(), s.begin(), ::tolower); });

    // Debug output:  Copy all data to std::cout
    std::copy(strings.begin(), strings.end(), std::ostream_iterator<std::string>(std::cout, "\n"));

    return 0;
}

This is the "more"-C++ way of implementing such a problem.

By the way, you can replace the istringstream and read from a file. No difference.