Glaze provides string interpolation for C++ structs through the stencil and mustache formats. These provide templating mechanisms for formatting structured data into strings, inspired by the Mustache templating language. This enables the generation of dynamic output by combining predefined templates with C++ structs.
Basic Usage¶
struct person { std :: string first_name {}; std :: string last_name {}; uint32_t age {}; bool hungry {}; bool employed {}; }; // Basic interpolation std :: string_view layout = R " ( {{first_name}} {{last_name}} is {{age}} years old ) " ; person p { "Henry" , "Foster" , 34 }; auto result = glz :: stencil ( layout , p ); // Result: "Henry Foster is 34 years old"
[!NOTE] result in these examples is a std::expected . Like most functions in Glaze (e.g. glz::write_json ) you can also pass in your own string buffer as the last argument, in which case the return type is glz::error_ctx .
Template Syntax Specification¶
Variable Interpolation¶
{{key}} - Replaces with the value of the specified field from the struct
- Replaces with the value of the specified field from the struct {{{key}}} - Triple braces for unescaped output (mustache format only)
Boolean Sections¶
{{#boolean_key}} CONTENT {{/boolean_key}} - Shows CONTENT if the boolean field is true
- Shows CONTENT if the boolean field is true {{^boolean_key}} CONTENT {{/boolean_key}} - Shows CONTENT if the boolean field is false (inverted section)
Container Iteration¶
{{#container_key}} TEMPLATE {{/container_key}} - Iterates over container elements, applying TEMPLATE to each item
- Iterates over container elements, applying TEMPLATE to each item {{^container_key}} CONTENT {{/container_key}} - Shows CONTENT if the container is empty
{{! This is a comment}} - Comments are ignored during template processing
Boolean Sections¶
std :: string_view layout = R " ( {{first_name}} {{last_name}} {{#employed}}Status: Employed, Age: {{age}}{{/employed}} ) " ; person p { "Carol" , "Davis" , 30 , true , true }; auto result = glz :: stencil ( layout , p ); // Result: "Carol Davis Status: Employed, Age: 30"
Inverted Sections¶
std :: string_view layout = R " ( {{first_name}} {{last_name}} {{^hungry}}I'm not hungry{{/hungry}} ) " ; person p { "Henry" , "Foster" , 34 , false }; // hungry is false auto result = glz :: stencil ( layout , p ); // Result: "Henry Foster I'm not hungry"
Container Iteration¶
struct TodoItem { std :: string text ; bool completed ; std :: string priority ; size_t id ; }; struct TodoList { std :: string title ; std :: vector < TodoItem > items ; bool has_items ; }; std :: string_view layout = R " ( {{title}}: {{#items}}{{text}} ({{priority}}) {{/items}} ) " ; TodoList list { "My Tasks" , {{ "Buy milk" , false , "normal" , 1 }, { "Call mom" , true , "high" , 2 }}, true }; auto result = glz :: stencil ( layout , list ); // Result: "My Tasks: Buy milk (normal) Call mom (high) "
Nested Sections¶
std :: string_view layout = R " ( {{#items}}{{text}} {{#completed}}✓{{/completed}}{{^completed}}○{{/completed}} {{/items}} ) " ; TodoList list { "Mixed Tasks" , {{ "Task 1" , false , "high" , 1 }, { "Task 2" , true , "low" , 2 }}, true }; auto result = glz :: stencil ( layout , list ); // Result: "Task 1 ○Task 2 ✓"
Empty Container Handling¶
std :: string_view layout = R " ( {{title}}{{^items}} - No items found{{/items}} ) " ; TodoList empty_list { "Empty List" , {}, false }; auto result = glz :: stencil ( layout , empty_list ); // Result: "Empty List - No items found"
Mustache Format¶
Glaze provides glz::mustache with the same interface as glz::stencil , but with HTML escaping behavior:
Double braces {{key}} - HTML-escaped output (safe for HTML)
- HTML-escaped output (safe for HTML) Triple braces {{{key}}} - Unescaped output (raw HTML)
HTML Escaping Examples¶
struct html_content { std :: string title ; std :: string raw_html ; }; // Double braces escape HTML std :: string_view layout = R " (