Fix parsing of std::vector and add test, example and documentation (#182)

Improve parsing into std::vector so that a single argument can take a list.

README.md

@@ -116,6 +116,18 @@ There is no way to disambiguate positional arguments from the value following
 a boolean, so we have chosen that they will be positional arguments, and
 therefore, `-o false` does not work.
 
+## `std::vector<T>` values
+
+Parsing of list of values in form of an `std::vector<T>` is also supported, as long as `T`
+can be parsed. To separate single values in a list the definition `CXXOPTS_VECTOR_DELIMITER`
+is used, which is ',' by default. Ensure that you use no whitespaces between values because
+those would be interpreted as the next command line option. Example for a command line option
+that can be parsed as a `std::vector<double>`:
+
+~~~
+--my_list=1,-2.1,3,4.5
+~~~
+
 ## Custom help
 
 The string after the program name on the first line of the help can be

include/cxxopts.hpp

@@ -44,6 +44,10 @@ THE SOFTWARE.
 #define CXXOPTS_HAS_OPTIONAL
 #endif
 
+#ifndef CXXOPTS_VECTOR_DELIMITER
+#define CXXOPTS_VECTOR_DELIMITER ','
+#endif
+
 #define CXXOPTS__VERSION_MAJOR 2
 #define CXXOPTS__VERSION_MINOR 2
 #define CXXOPTS__VERSION_PATCH 0
@@ -715,9 +719,13 @@ namespace cxxopts
     void
     parse_value(const std::string& text, std::vector<T>& value)
     {
-      T v;
-      parse_value(text, v);
-      value.push_back(v);
+      std::stringstream in(text);
+      std::string token;
+      while(in.eof() == false && std::getline(in, token, CXXOPTS_VECTOR_DELIMITER)) {
+        T v;
+        parse_value(token, v);
+        value.emplace_back(std::move(v));
+      }
     }
 
 #ifdef CXXOPTS_HAS_OPTIONAL

src/example.cpp

@@ -56,6 +56,7 @@ parse(int argc, char* argv[])
       ("help", "Print help")
       ("int", "An integer", cxxopts::value<int>(), "N")
       ("float", "A floating point number", cxxopts::value<float>())
+      ("vector", "A list of doubles", cxxopts::value<std::vector<double>>())
       ("option_that_is_too_long_for_the_help", "A very long option")
     #ifdef CXXOPTS_USE_UNICODE
       ("unicode", u8"A help option with non-ascii: à. Here the size of the"
@@ -130,6 +131,16 @@ parse(int argc, char* argv[])
       std::cout << "float = " << result["float"].as<float>() << std::endl;
     }
 
+    if (result.count("vector"))
+    {
+      std::cout << "vector = ";
+      const auto values = result["vector"].as<std::vector<double>>();
+      for (const auto& v : values) {
+        std::cout << v << ", ";
+      }
+      std::cout << std::endl;
+    }
+
     std::cout << "Arguments remain = " << argc << std::endl;
 
     return result;

test/options.cpp

@@ -512,6 +512,26 @@ TEST_CASE("Booleans", "[boolean]") {
   REQUIRE(result.count("others") == 1);
 }
 
+TEST_CASE("std::vector", "[vector]") {
+  std::vector<double> vector;
+  cxxopts::Options options("vector", " - tests vector");
+  options.add_options()
+      ("vector", "an vector option", cxxopts::value<std::vector<double>>(vector));
+
+  Argv av({"vector", "--vector", "1,-2.1,3,4.5"});
+
+  char** argv = av.argv();
+  auto argc = av.argc();
+
+  options.parse(argc, argv);
+
+  REQUIRE(vector.size() == 4);
+  CHECK(vector[0] == 1);
+  CHECK(vector[1] == -2.1);
+  CHECK(vector[2] == 3);
+  CHECK(vector[3] == 4.5);
+}
+
 #ifdef CXXOPTS_HAS_OPTIONAL
 TEST_CASE("std::optional", "[optional]") {
   std::optional<std::string> optional;