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Templating (Mustache)

Templating is when you return an html page with custom data. You can probably tell why that's useful.

Crow supports mustache for templates through its own implementation crow::mustache.

Components of mustache

There are 2 components of a mustache template implementation:

  • Page
  • Context


The HTML page (including the mustache tags). It is usually loaded into crow::mustache::template_t. It needs to be placed in the templates directory which should be directly inside the current working directory of the crow executable.

For more information on how to formulate a template, see this mustache manual.


A JSON object containing the tags as keys and their values. crow::mustache::context is actually a crow::json::wvalue.


crow::mustache::context can take a C++ lambda as a value. The lambda needs to take a string as an argument and return a string, such as ctx[lmd] = [&](std::string){return "Hello World";};.

Returning a template

To return a mustache template, you need to load a page using auto page = crow::mustache::load("path/to/template.html");, keep in mind that the path is relative to the templates directory.
You also need to set up the context by using crow::mustache::context ctx;. Then you need to assign the keys and values, this can be done the same way you assign values to a json write value (ctx["key"] = value;).
With your context and page ready, just return page.render(ctx);. This will use the context data to return a filled template.
Alternatively you could just render the page without a context using return page.render();.