Format custom help message with configured column width

include/cxxopts.hpp

@@ -2300,6 +2300,58 @@ format_description
   return result;
 }
 
+String
+format_custom_help
+(
+  const std::string& custom_help,
+  std::size_t start,
+  std::size_t allowed
+)
+{
+  String result;
+  std::size_t count = 0;
+  std::size_t word_size = 0;
+
+  if(allowed <= start)
+  {
+    throw_or_mimic<exceptions::invalid_option_format>("Allowed column" 
+      "width must be greater than start column width!");
+  }
+
+  for (std::size_t i = 0; i < custom_help.length(); i++)
+  {
+    char c = custom_help[i];
+
+    while (count < start) {
+      result.push_back(' ');
+      count++;
+    }
+
+    // record the start of a word
+    word_size = (std::isspace(c)) ? 0 : word_size + 1;
+
+    result.push_back(c);
+
+    count = (c == '\n') ? 0 : count + 1;
+
+    if (count >= allowed)
+    {
+      // if we are in the middle of a word, backtrack until word_size is 0
+
+      for (std::size_t c1 = 0; c1 < word_size; c1++)
+      {
+        result.pop_back();
+        i--;
+      }
+
+      result.push_back('\n');
+      count = 0;
+    }
+  }
+
+  return result;
+}
+
 } // namespace
 
 inline
@@ -2886,6 +2938,7 @@ Options::help(const std::vector<std::string>& help_groups, bool print_usage) con
   if (!m_custom_help.empty())
   {
     result += " " + toLocalString(m_custom_help);
+    result = format_custom_help(result, OPTION_DESC_GAP, m_width);
   }
 
   if (!m_positional.empty() && !m_positional_help.empty()) {

test/options.cpp

@@ -1191,3 +1191,39 @@ TEST_CASE("No Options help", "[options]")
   CHECK_NOTHROW(options.parse(argc, argv));
   CHECK(options.help().find("test <posArg1>...<posArgN>") != std::string::npos);
 }
+
+TEST_CASE("Format custom message with selected width", "[help]")
+{
+  cxxopts::Options options("Custom message width",
+                           " - test custom message formatting width");
+
+  options.custom_help(
+    "A very very long description that should be wrapped according to the "
+    "specified width for help messages. This is to ensure that lines are not "
+    "very long and remain readable. Just to make sure we have enough text here "
+    "to trigger the wrapping functionality properly. Let's add a bit more text "
+    "to be certain!");
+
+  options.set_width(60);
+  const auto help = options.help();
+  CHECK(
+    help.find(
+        "Custom message width A very very long description that \n  should "
+        "be wrapped according to the specified width for \n  help messages. "
+        "This is to ensure that lines are not very \n  long and remain "
+        "readable. Just to make sure we have \n  enough text here to trigger "
+        "the wrapping functionality \n  properly. Let's add a bit more text "
+        "to be certain!") != std::string::npos);
+
+  options.set_width(90);
+  const auto help90 = options.help();
+  CHECK(
+    help90.find(
+        "Custom message width A very very long description that should be "
+        "wrapped according to \n  the specified width for help messages. "
+        "This is to ensure that lines are not very long \n  and remain "
+        "readable. Just to make sure we have enough text here to trigger the "
+        "wrapping \n  functionality properly. Let's add a bit more text to "
+        "be certain!") !=
+    std::string::npos);
+}