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Templates: Rendering Commands (v 1.x)


The simplest templates command is showing variable. The syntax is trivial:


For example, if you want to show a content value message just write:

<%= message %>

It is actually translated to C++ code:


Where escape function writes the message member variable of the content to the stream and escapes special HTML characters <, >, &, " with their HTML representations like &lt;

If you want to get a value of some property, you just write.

<%= some_property() %>

Which is translated to:


Note: since CppCMS 1.1 it is possible to change default filter using filter block.

Variable with filters

You can add arbitrary filters to the variable you show. The syntax is following:

'=' VARIABLE [ '|' filter [ '|' filter ] ... ]

Where filter is

[ 'ext' ] NAME [ '(' ( VARIABLE | STRING | NUMBER ) [ ',' ( VARIABLE | STRING | NUMBER ) ] ... ]


If no filters, are given the variable is automatically escaped, but if you provide any filter they are used instead of escaping.

Each variable is actually a creation or call of special filter object with given parameters, where first parameter is the "filtered" variable and others are filter parameters. For example:

<%= birthday | strftime("%d/%m/%Y") %>

Is translated into:


You can also concatenate filters using pipe symbol:

<%= birthday | strftime("%d %m %Y") | urlencode %>

Would be rendered as:


There is a set of filters predefined available for you, see cppcms::filters namespace reference.

One of the filters that is worth to noticing is raw: it allows to write a variable as-is, without any HTML escaping.

<%= ready_html | raw %>

The ready_html variable will be written as-is to the output stream without escaping HTML symbols like <.

You can specify arbitrary external filters that are defined in content class. For example:

namespace data {
  struct page {
  virtual string bbcode(string const &);

Then in template we can specify:

<% class page uses data::page %>
  <% template render() %>
    <%= message | ext bbcode %>
  <% end %>
<% end %>

Note: Under Windows platform, dynamically loaded libraries (dll) do not allow undefined symbols. Thus, if you want to support Windows, you should create your filters as virtual functions or callbacks like booster::function<> in order to prevent referring to external symbol.

Variable - Deprecated Syntax

CppCMS supports older deprecated syntax (without "="):

VARIABLE [ '|' filter [ '|' filter ] ... ]

However it is not recommended due to fact that new template keywords may be introduced that would hide the existing variable and cause syntax error.

Default Escape Filter Block

Since: CppCMS 1.1

Block command filter allows in its current scope to change the default escape filter to a different one:

filter [ ext ] VARIABLE 

For example

<p>Hello <%= name %></p>
<% filter jsescape %>    
  var name = "<%= name %>";
  alert('Hello ' + name);
<% end %>
<p>You work at <%= job %></p>

First appearance of name would be escaped using standard HTML escape filter and the second one would allow safely include the text in JavaScript or JSON strings.

Upon end of filter block the filter is reverted to previous thus job would be escaped again using default HTML filter.

By pre-pending the filter name with ext it is possible to use a filter defined at content level - custom external filter.

Note: it does not change default urlencode filter for <% url ... %> commands



'gt' STRING [ 'using' using-options ]
'ngt' STRING ',' STRING ',' VARIABLE [ 'using' using-options ]
// since 1.2
'gt' STRING [',' STRING ] [ 'using' using-options ]
'ngt' STRING ',' STRING [',' STRING ] ',' VARIABLE [ 'using' using-options ]

Where using-options is:

display-variable-block [ ',' display-variable-block [ ',' ... ] ]

Where display-variable-block is any variable of optional filters as described above. For example:

<% gt "Press the button" %>
<% gt "Hello Dear {1}, we are glad to see you!" using name %>
<% gt "Hello <a href=\"{1}\">{2}</a> you have {3}" using link | urlencode , name , something %>
<% ngt "You have one apple","You have {1} apples",n using n %>


gt -- gettext translates given string according to locale defined in the output stream. For example:

<% gt "Press the button" %>

Would be translated as "Press the button" in English locale and "Нажмите кнопку" under Russian locale.

You can specify additional parameters using using option. You provide a list of comma separated values as you would display a variable. You can use any other filters as usual. "{1}", "{2}" etc, specify the order of input variables. It uses booster::locale::format or cppcms::locale::format for such substitutions (according to localization backend CppCMS compiled with.)

ngt -- ngettext translate plural form for given integer. Where first parameter is single form, second plural and the third should be the variable is used.


  1. When you use ngt you encouraged to use using syntax, because you should provide an actual number to display.
  2. You may use <% if rtl %> or <% if not rtl %> in order to test direction of text. This is actually equivalent to:

     <% if (cppcms::locale::gettext("LTR",out().getloc())=="RTL") %>

    See if statement for further description.

Since 1.2: it is possible to add a context to help the translation as the first element of gt and ngt commands:

<% gt "form element", "Use the button" %>
<% gt "clothing", "Use the button" %>
<% ngt "form element", "there is one button","there are {1} buttons", n using n %>
<% ngt "form element", "there is one button","there are {1} buttons", n using n %>
<% ngt "closthing", "there is one button","there are {1} buttons", n using n %>

That will show by default "Use the button" in English but may require different translation for different types of buttons one for UI and one for clothing.

URL Mapping


'url' STRING [ 'using' using-options ]

Where using-options is:

display-variable-block [ ',' display-variable-block [ ',' ... ] ]

Where display-variable-block is any variable of optional filters as described above. For example:

For example:

<% url "/blog/summary"  %>
<% url "../summary"  %>
<% url "/blog/post" using post_id %>
<% url "/blog/post" using post_id , slug | ext filter_for_url %>


The url tag is a templates interface to cppcms::url_mapper interface accessible from the cppcms::application

This tag allows to access to abstract URLs of the application with given parameters. To learn how to use URL mapping read the description of url_mapper class given above.

The using parameters are passes for the formatting of the URL parameters.

Note: unlike the variable rendering the default escaping for the parameters is urlencode and not escape

For example

<% url "/blog/post" using slug %>
<p>Where slug is "Hi <you>" would generate something like</p>

and not

"/myblog/Hi &lt;you&gt;/"

Including other templates


'include' IDENTIFIER '(' [ parameter [ ',' parameter ...] ] ')' [ 'from' IDENTIFIER | 'using' IDENTIFIER [ 'with' VARIABLE ] ]

Where parameter is one of VARIABLE, STRING or NUMBER. For example:

<% include title() %>
<% include parent::foo() %>
<% include bar(x,"test",-1.0) from foo %>
<% include bar(x,"test",-1.0) using baz %>


This command allows inclusion of other templates in place (actually calling other member functions.) You can include existing implementation in parent views in order to extend them. For example:

<% view master uses data::master %>
  <% template menu() %>
    <li><a href="#1">Main</a></li>
    <li><a href="#2">Products</a></li>
  <% end template %>
  <% template render() %>
    <ul><% include menu() %></ul>
  <% end template %>
<% end view %>
<% view sales uses data::sales extends master %>
  <% template menu() %>
    <% include master::menu() %>
    <li><a href="#3">Orders</a></li>
  <% end %>
<% end %>

The above code extends menu for view sales with an additional option.

The from option allows to include templates from locally initialized views withing using blocks.

For more details read Views Helpers section

Rendering Forms


'form' ('as_p' | 'as_table' | 'as_ul' | 'as_dl' | 'as_space' | 'input' | 'block' | 'begin' | 'end' ) VARIABLE

as_* flags allow you to render cppcms::form, with specific delimiters, when input, begin, end and block flags allow you to render single part of the widget.


Forms are organized as form object or sets of widgets. Each set can be rendered using different delimiters:

For example:

<% form as_table form.fields %>
<p><% form as_space form.submit_buttons %></p>

May be rendered as:

<tr><th>User Name:</th><td><input ... /></td></tr>
<tr><th>Password: </th><td><input ... /></td></tr>
<p><input ... value="Login" /> <input ... value="Forgot Password" /></p>

Sometimes you want to perform custom rendering of widgets that is not predefined by this list. In such case you may render only <input ...> field of the widget by calling

<% form input some_button %>

Which would be rendered like this:

<input type="submit" name="_3" value="Press" />

Note, input does not strictly means that it is limited for widgets using HTML input tag, it works for any other widget just limited to actual content rendering without "help" messages, for example, for widget cppcms::widgets::textarea it would be <textarea ...>some text</textarea>

Sometimes you need even more fine grained access to widget rendering parts, for example you may want to add some attributes to the widget in the view.

You may render begin or end part of the widget, such that you can insert HTML attributes between them or even JavaScript.

<% form begin some_button %> onclick="return foo()" <% form end some_button %> 

Which would be rendered as

<input type="submit" name="_3" onclick="return foo()" value="Press" />

Alternatively it can be shortened to

<% form block some_button %> onclick="return foo()" <% end %>

Which is much shorter and more clear syntax that is recommended for the use. It is implemented starting from CppCMS 0.99.12.

For generation of custom HTML for widgets you can always use widget properties directly:

<input type="submit" name="<% %>" value="Press" /> ( <% %> )

See: cppcms::widgets namespace for documentation of each specific widget properties.

CSRF Prevention

When using forms it is important to prevent an attempts of CSRF. It is possible by setting security.csrf.enable settings value to true and by including a special CSRF token.


'csrf' ['token' | 'cookie' | 'script' ]



By default <% csrf %> inject a hidden form input that contains a session specific token. It is used like this:

<form method="post" action="/path/to"><% csrf %>
  <% form as_p my_form %>

It creates a hidden input that keeps this token.


  1. it must be used only on POST forms and never on GET forms as it would disclose the token in the referrer url.
  2. Caching pages the generated token would be invalid as it would be cached for some used and would not be session specific.

    In such case it is possible to set settings value to true and it would keep the CSRF token in a special cookie, this cookie value should be used as CSRF token.

    The cookie name can be fetched using cookie option.

    It is also possible to inject a short javascript code that would read the cookie and dynamically generate the input form. This way it would be safe to use it with cached pages.

Rendering other views

Implemented in CppCMS 0.99.12


'render' [ ( VARIABLE | STRING ) , ] ( VARIABLE | STRING ) [ 'with' VARIABLE ]


This function allows to render different views by their names that can be defined in constant strings or in variables allowing dynamic selection of views/skins.

If the skin name is not provided current skin is used.

The optional parameter is the content that is rendered. If no content given current "this" content is used.

For example:

<% render "sidebar" with sidebar_data %>
<% render skin_name, "sidebar" with sidebar_data %>

Views Helpers

Implemented in CppCMS 0.99.12


This command is block command that comes in pair with <% end %> block.

'using' IDENTIFIER  [ 'with' VARIABLE ] as IDENTIFIER [ 'from' (VARIABLE|STRING) [, (VARIABLE|STRING) ] ] // since 1.2


For example:

<% using foo with some_content as bar %>
  <% include baz() from bar %>
  <% include beep(10) from bar %>
<% end using %>

The using block creates local view object bar of a type foo that uses some_content as the content for the rendering.

This local object bar can be accessed using include command with from syntax. So technically the example above is something like (after removing some details)

  foo bar(content.some_content);

This is very useful for creating "helper" views that include common routines or patterns.

If with part is not defined the current content is used as the content that should be rendered.

If you need to call only a single function of some helper view there is a simple shortcut:

<% include baz() using foo with some_content %>

Which is equivalent to:

<% using foo with some_content as _some_variable %>
   <% include baz() from _some_variable %>
<% end using %>

Since 1.2:

from part allows to select dynamically a view by name or view by name from certain skin by name. It should be derived from the view specified as first parameter.

For example:

<% using master_api as m from a_skin, "api" %>

Define m as "api" view defined in skin selected by variable a_skin. Note "api" should be derived from master_api

Selecting HTML/XHTML

You may request generation HTML or XHTML code in forms using following command:

( 'xhtml' | 'html' )

Note, this command has global effect on all template without connection to specific class. You should include it in the topmost class of your view.

<% c++ #include "all_data.h" %>
<% xhtml %>
<% skin %>
<% view master uses data::master %>
<% template render() %>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN"

Currently, this option affects only forms code generation.

Selecting localization domain

Since 1.2:

You can select localization domain using following command


Note, this command has global effect on all views and is defined globally for all skin.

<% c++ #include "all_data.h" %>
<% domain my_domain %>
<% skin my_skin %>

Injecting C++ Code

You can always inject any kind of C++ code using:

"c++" any-c++-statement

For example:

<% c++ #include "all_content.h" %>


  1. If you want to refer to content variables in your code, do not forget to use content member of your class. For example:

     <%= a %> + <%= b %> = <% c++ out()<<content.a+content.b; %>
  2. Generally you should not use C++ code in template, use it if it is absolutely necessary.
  3. If you want use special conditions prefer specialized if statement over <% c++ if() { %>...<% c++ } %>


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