Read from istream with possible '\n' symbols

Question

I need to read from istream some strings, of which there are two types:

1. " strings with leading and trailing spaces " which should look like "strings with leading and trailing spaces" (only leading and trailing spaces are trimmed, what's within them is kept)
2. " John Doe \n Mary Smith". Here I need to a) read only until the '\n' and b) delete the leading spaces while retaining the trailing spaces so the string I get is "John Doe " (mind that the trailing spaces are still there).

I got confused about how I can read the line and get to know if there are more that one '\n' in it.

Answer 1

You can read the string with std::getline, and if it is multiline, then leave trailing spaces, if not, remove them too:

#include <iostream>
#include <string>
#include <sstream>

int main()
{
    //std::istringstream iss("   strings with leading and    trailing spaces   ");
    std::istringstream iss("  John Doe    \n  Mary Smith");

    std::string lines[2];
    size_t i = 0;
    bool keep_trailing_spaces = false;
    while (std::getline(iss, lines[i++], '\n'))
    {
        if (i > 1)
        {
            keep_trailing_spaces = true;
            break;
        }
    }

    if (i > 1)
    {
        size_t start = lines[0].find_first_not_of(' ');
        size_t count = keep_trailing_spaces ? std::string::npos : lines[0].find_last_not_of(' ') - start + 1;

        std::cout << ">" << lines[0].substr(start, count) << "<" << std::endl;
    }

    return 0;
}

https://ideone.com/tLBiSb

1st result: >strings with leading and trailing spaces<

2nd result: >John Doe <