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Difference "cppcms::base_view & cppcms::base_content" ver. 4 versus ver. 5


## cppcms::base\_content
This is a simple polymorphic class from which every cppcms content template should be derided. It allows dynamic casting of the content for the target application:
class base_content {
virtual ~base_content() {};
## cppcms::base\_view
### Members
- **`worker_thread &worker`** -- reference to the worker thread that called the rendering procedure.
- **`ostream &cout`** -- reference to the output stream that output is rendered to.
### How Derived Classes are created:
This is the class that every view generated from the template system is derived from.
Every derived class defines the important public member --- `content` --- the reference to the user defined content class.
It also creates member functions for each implemented template. For example:
<% c++ #include "data.h" %>
<% namespace my_view %>
<% class message uses data::message %>
<% template render() %>
<h1><% message %> World!</h1>
<% end template %>
<% end class %>
<% end namespace %>
The above template is rendered to C++ output:
#include "data.h"
namespace my_view {
struct message :public cppcms::base_view
data::message &content;
cppcms::transtext::trans const *tr;
message(cppcms::base_view::settings _s,data::message &_content):
virtual void render() {
" <body>\n"
" <h1>";
cout<<" World!</h1>\n"
" </body>\n"
} // end of template render
}; // end of class message
} // end of namespace my_view
### Member functions
#### Default filter
template<typename T>
string escape(T const &v)
This is the default filter. It performs the rendering of the input parameter to text. This function is always called when the template parameter is substituted without filters, i.e.:
<% param %>
is converted to
By default, it uses `ostream` to render the output, however it provides several specializations:
- **`string escape(string const &s)`** -- performs HTML escaping of string.
- **`string escape(std::tm const &v)`** -- converts `std::tm` time to human readable format.
#### Provided Filters
They are called when some filters are given. Each filter has the following possible signatures:
string filter_name(Type const &inp);
string filter_name(Type const &inp,string param);
Where `inp` is a given filter input and `param` is the filter parameter.
- **`string raw(string s)`** -- raw filter, does nothing. It is used to push some html data without escaping. For example:
<% some_html_page | raw %>
- **`string intf(int val,string f)`** -- format integer number. It uses `boost::format` for this purpose. For example:
Decimal <% num %> is hexadecimal <% num | intf("%x"); %>
- **`string strftime(std::tm const &t,string f)`** -- formats the output string using std::strftime call. For example:
<% date | strftime("%d/%m/%Y") %>
It has tho following "shortcuts" for showing the date only, the time or the time with seconds:
string date(std::tm const &t);
string time(std::tm const &t);
string timesec(std::tm const &t);
- **`string urlencode(string const &s);`** -- encode string for URL. For example:
<a href="http://site/article/<% link | urlencode %>">
#### Other member functions
boost::format format(string const &f);
Function that returns i\a `boost::format` object constructed with `f` and with disabled exceptions. In generally `boost::format` throws an exception in case of an incorrect format or parameters list --- this is not such a good behavior for displaying various data.
It is used mostly by gettext and ngettext implementations. For example
<% ngt "We have one apple","We have %1% apples",n using n %>
Is rendered to:
cout<<format(tr->gettext("We have one apple","We have %1% apples",n)) % escape(n);
Thus it would not throw an exception in case of "one apple".
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## Releated
- [cppcms::application](/wikipp/en/page/ref_cppcms_application)
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