C++ Retrieving Several Lines From a String

Question

One of my assignments involves reading several strings into my program. I've figured out how to store the strings into one, but now I need to retrieve each string by line. Any suggestions? Example:

string s = "Hello
            Welcome
            Oranges
            Bananas
            Hi
            Triangle"

I'm not allowed to store them into an array either; they must all be contained in one string.

A lot of ways: https://stackoverflow.com/questions/236129/the-most-elegant-way-to-iterate-the-words-of-a-string — NathanOliver, Oct 08 '18 at 19:55
Use a separator, like $ or anything else that you can search for and then split by. — Fausto Carvalho Marques Silva, Oct 08 '18 at 19:57
This smells like homework but you haven't show any effort. Not even your description is clear. — Ulrich Eckhardt, Oct 08 '18 at 19:58
Also this is not valid C++ by current C++17 standard. You have to use \n not type newlines. — Öö Tiib, Oct 08 '18 at 20:01
@ÖöTiib Nothing to do with c++17 standard. Continued string literals where ever accepted, to keep the newlines in place you just need to put an `\` escape character at the end of each line. — πάντα ῥεῖ, Oct 08 '18 at 20:24
This is homework, but I'm not allowed to modify the string itself. I'm just supposed to retrieve each string from each line. — Bagman, Oct 08 '18 at 21:06

Jerry Coffin · Answer 1 · 2018-10-08T20:05:00.587

1

I would probably put the string into stringstream, then use something like std::getline to read a line at a time from the string stream. If you're really worried about execution speed, there are faster ways, but that would be the obvious first choice until profiling told you it wasn't allowable.

For what it's worth, to embed a new-line into the string, you can use either \n, or switch to using a raw string literal:

string s = R"(Hello
              Welcome
              Oranges
              Bananas
              Hi
              Triangle)";

With a raw string literal, embedded new-lines (and anything else) becomes part of the string itself. In a normal string literal, you have to use \n instead (if you want it to be portable, anyway).

edited Oct 08 '18 at 20:05

answered Oct 08 '18 at 19:59

Jerry Coffin

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Good attempt, but my answer covers the parenthesis as well now ;-) – πάντα ῥεῖ Oct 08 '18 at 20:21
1

@πάνταῥεῖ: Covers a case that's not requested by the OP, but adds another case (not requested by the OP either) for which it fails. Doesn't seem like a huge improvement to me, but perhaps it's useful. As a rule, I don't favor posting a complete solution to obvious homework though. – Jerry Coffin Oct 08 '18 at 20:56

πάντα ῥεῖ · Answer 2 · 2018-10-08T20:35:56.840

To render std::string content as is use a raw string literal. The following code would retrieve all single lines from a raw string literal:

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

int main() {
   std::string s = R"x(Hello
Welcome
Oranges
Bananas
Hi
Triangle (and hey, some extra stuff in the line with parenthesis)
)x"; 
    std::istringstream iss(s); 
    std::vector<std::string> lines; 
    std::string line; 
    while(getline(iss,line)) { 
        lines.push_back(line); 
    }
    for(const auto& line : lines) {
        std::cout << line << '\n';
    }
}

See the working version online here.

With prior c++11 standards, you'll have to escape the line breaks with a \ character like so:

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

int main() {
   std::string s = "Hello \n\
Welcome \n\
Oranges \n\
Bananas \n\
Hi  \n\
Triangle (and hey, some extra stuff in the line with parenthesis)"; 
    std::istringstream iss(s); 
    std::vector<std::string> lines; 
    std::string line; 
    while(getline(iss,line)) { 
        lines.push_back(line); 
    }
    for(std::vector<std::string>::const_iterator it = lines.begin(); it != lines.end(); ++it) {
        std::cout << *it << '\n';
    }
}

See the other working online example.

C++ Retrieving Several Lines From a String

2 Answers2