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Difference "Tutorial: Using Templates (v 1.x)" ver. 24 versus ver. 25


## Introduction
CppCMS is an [MVC]( web framework. One of its important parts is view - the HTML rendering system.
CppCMS's web pages are written in a special template language, that is translated to C++ code that can be compiled to a shared object (or DLL on windows) or be statically linked into your applications.
Generally the CppCMS template system uses a push model, where the user application prepares the content and pushes it to the web template system for rendering.
For proper rendering of templates two stages are required:
1. Your application (controller) prepares the "content" for the HTML template system.
2. The content returned to the users is rendered to HTML using the template system.
## Code
In order to work with templates we need to separate our
source into three parts:
- The content - the objects which are filled with the data that should be rendered.
- The application itself which creates the content.
- The HTML template which renders the content.
### The content
The content declarations will appear in the "content.h" file:
#include <cppcms/view.h>
#include <string>
We need to include the header `<cppcms/view.h>` that will provide us with all the definitions required as a base for our content class.
namespace content {
struct message : public cppcms::base_content {
std::string text;
Each content object should be derived from the class `cppcms::base_content` and should store all relevant data.
So we've created a small structure '`message`' that holds a single string `text` that will be rendered with an HTML template.
As a rule of thumb we put all our content objects in a
separate namespace.
### The template
All web templates are separated into skins - the specific implementation of the view that can vary for the same content. Each skin is placed in the namespace with the same name.
Each skin consists of a set of views - the representation of a single page. All views can be organized into a hierarchy of views. Each view can extend the base view with more features and redefine its templates. The views are represented with classes, each one of them being responsible for rendering a specific content object.
As a rule of thumb we name them the same way as the corresponding content classes.
Each view consists of a set of templates. The base template, which is always rendered, is called `render`. `render` should always be implemented.
So lets see out first template:
<% c++ #include "content.h" %>
<% skin my_skin %>
<% view message uses content::message %>
<% template render() %>
<h1><%= text %> World!</h1>
<% end template %>
<% end view %>
<% end skin %>
In the first line we use C++ inline code to include the appropriate header.
Then we define our skin called simply "my_skin" and then in line 3 we define our view. We call it "message", the same as our content's class. We declare that is would render an object of type '`content::message`'.
Then in line 4 we define the function that actually renders all the HTML for us - `render`.
On line 7 we display a member `text` of the `content::message` in the HTML. Note: the displayed text
will be automatically escaped with HTML entities, for example `<` will be converted into `&lt;`.
### The controller
Similarly to our "hello world" example we define the `main` function of our application. Before this, we have included our `content.h` header.
Our main function:
Our headers:
virtual void main(std::string /*url*/)
content::message c;
#include <cppcms/application.h>
#include <cppcms/applications_pool.h>
#include <cppcms/service.h>
#include <cppcms/http_response.h>
#include <cppcms/url_dispatcher.h>
#include <iostream>
#include "content.h"
Our main class:
class my_hello_world : public cppcms::application {
my_hello_world(cppcms::service &s) :
virtual void main(std::string /*url*/)
content::message c;
Our main function:
int main(int argc,char ** argv)
try {
cppcms::service srv(argc,argv);
catch(std::exception const &e) {
We create an object `c` of type `content::message`
and set the value for its `text` member with an
arbitrary HTML unsafe string.
Then we call the `render` member function of `cppcms::application` with the following parameters:
1. The name of the view for the default skin. It generally matches the name of the content class, in our case "message".
2. The content object itself that holds all of the data that the HTML template needs.
After calling it, the HTML will automatically be written
to the output.
## Building Templates
The template shown above should be compiled into C++ code in order to be useful. We do this with a special compiler, as follows:
cppcms_tmpl_cc my_skin.tmpl -o my_skin.cpp
The created `my_skin.cpp` contains all the code needed for rendering and registering this skin in CppCMS's rendering system.
### Linking Statically
Now, `my_skin.cpp` should be compiled and linked together with your application:
g++ hello.cpp my_skin.cpp -o hello -lcppcms -lbooster
And we can run our application as usual:
./hello -c config.js
### Dynamic loading
Dynamic linking is a little bit more tricky, but it is much more powerful as it allows you to load skins without relinking the application. You can even update your application without needing to restart it.
First we create a shared object from our `my_skin.cpp` file, and name it with the same name as our skin:
g++ -shared -fPIC my_skin.cpp -o -lcppcms -lbooster
(Or for GCC 4.7 on OSX, we create it like this:)
g++ -shared -fPIC my_skin.cpp -o libmy_skin.dylib -lcppcms -lbooster
Now we compile our hello application without `my_skin.cpp` but we pass an additional parameter `-rdynamic` in order to allow shared library to see symbols in the application:
g++ -rdynamic hello.cpp -o hello -lcppcms -lbooster
(Or for GCC 4.7 on OSX, we compile it like this:)
g++ -dynamic hello.cpp -o hello -lcppcms -lbooster
Now our system is almost ready to run, we just need to add
into our configuration description which skins should be loaded dynamically. We add the following section to `config.js`:
"views" : {
"paths" : [ "." ],
"skins" : [ "my_skin" ]
- `paths` - describes the location of the dynamic libraries that should be loaded.
- `skins` - describes the list of skins that should be loaded.
Now run the application as usual and it will load the
skins and use them.
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