S03. Use Path Parameters

For dynamic URLs like /users/:id — the staple of REST APIs — just put :name in the path pattern. The matched values end up in req.path_params.

Basic usage

svr.Get("/users/:id", [](const httplib::Request &req, httplib::Response &res) {
  auto id = req.path_params.at("id");
  res.set_content("user id: " + id, "text/plain");
});

A request to /users/42 fills req.path_params["id"] with "42". path_params is a std::unordered_map<std::string, std::string>, so use at() to read it.

Multiple parameters

You can have as many as you need.

svr.Get("/orgs/:org/repos/:repo", [](const httplib::Request &req, httplib::Response &res) {
  auto org = req.path_params.at("org");
  auto repo = req.path_params.at("repo");
  res.set_content(org + "/" + repo, "text/plain");
});

This matches paths like /orgs/anthropic/repos/cpp-httplib.

Regex patterns

For more flexible matching, use a std::regex-based pattern.

svr.Get(R"(/users/(\d+))", [](const httplib::Request &req, httplib::Response &res) {
  auto id = req.matches[1];
  res.set_content("user id: " + std::string(id), "text/plain");
});

Parentheses in the pattern become captures in req.matches. req.matches[0] is the full match; req.matches[1] onward are the captures.

Which to use

• For plain IDs or slugs, :name is enough — readable, and the shape is obvious
• Use regex when you want to constrain the URL to, say, numbers only or a UUID format
• Mixing both can get confusing — stick with one style per project

Note: Path parameters come in as strings. If you need an integer, convert with std::stoi() and don't forget to handle conversion errors.