Simple parser for SVG Polgon points.

points.cpp

#include <cstdlib>
#include <iostream>
#include <locale>
#include <string>
#include <vector>

bool is_whitespace(char value)
{
    // Values are defined in the SVG specification.
    return (value == '0x9') ||
           (value == '0xD') ||
           (value == '0xA') ||
           (value == '0x20');
}

std::size_t skip_comma(const std::string & str, std::size_t start_index)
{
    while (start_index < str.length())
    {
        if ((str[start_index] != ',') && !is_whitespace(str[start_index]))
        {
            break;
        }
        ++start_index;
    }
    return start_index;
}

double get_double(const std::string & str, std::size_t start_index, std::ptrdiff_t & consumed)
{
    const char * start = str.data() + start_index;
    char * end = const_cast<char*>(start);
    double parsed = std::strtod(start, &end);

    consumed = end - start;
    return parsed;
}

std::vector<double> get_points(const std::string & input)
{
    std::vector<double> output;
    std::size_t index = 0U;
    std::ptrdiff_t consumed = 0;

    while (index < input.length())
    {
        double value = get_double(input, index, consumed);
        if (consumed == 0)
        {
            break;
        }

        output.push_back(value);
        index = skip_comma(input, index + consumed);
    }
    return output;
}

// Exmaple usage
void display_points(const std::string & input)
{
    auto points = get_points(input);
    std::cout << "'" << input << "' - ";
    for (auto it = points.cbegin(); it != points.cend(); ++it)
    {
        std::cout << *it << "  ";
    }
    std::cout << "\n";
}

int main()
{
    display_points("0, 0  -10, 0  -5, -10");
    display_points("0,0 -10,0 -5,-10");
    display_points("0,0,-10,0,-5,-10");
    display_points("0 0 -10 0 -5 -10");
    display_points("0 0-10 0-5-10");
    display_points("0-0-10-0-5-10");
    system("PAUSE");
    return 0;
}