How can I extract integers from a string?

Question

Consider a string of the form

"number of columns = 5
number of rows = 345
1 3 -5 2 9
4 -10 34 -22 7"

[There are 343 more rows followed by this. However, I guess it will be enough to explain the problem.]

I wish to extract the values 5 and 345 as integers. The substrings "number of columns = " and "number of rows = " are known but the number of digits in the values followed by these strings is not known. However, it is known that the corresponding line ends after the value. I can get to the beginning of the number using the following code

std::string searchString = "clause length = ";
int searchStringLength = searchString.length();
std::size_t startAt = result.find(searchString) + searchStringLength;

However, I don't know how to detect the end of a line, using which I can extract the values.

And the next part is to extract the rest of the integers and store them in an array and I think if I can identify the positions of the empty spaces and the end of lines, this problem will also get resolved.

How can I solve this problem efficiently [I am using Visual Studio 2017]?

Answer 1

Try the following simple number extractor based on regex

#include <iostream>
#include <iterator>
#include <string>
#include <regex>

int main()
{
    std::string s = "number of columns = 5\n"
        "number of rows = 345\n"
        "1 3 -5 2 9\n"
        "4 -10 34 -22 7\n";

    std::regex num_regex("\\d+|-\\d+");
    auto num_begin = 
        std::sregex_iterator(s.begin(), s.end(), num_regex);
    auto num_end = std::sregex_iterator();

    for (std::sregex_iterator i = num_begin; i != num_end; ++i) {
        std::smatch match = *i;
        std::string match_str = match.str();
        std::cout << "  " << match_str << '\n';
    }

}

Output

  5
  345
  1
  3
  -5
  2
  9
  4
  -10
  34
  -22
  7

Answer 2

You can split the string into tokens. In this case split the string according to "=" sign and then try to convert them into integer's http://www.cplusplus.com/reference/cstring/strtok/ Go through this link