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## Introduction
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Now we will learn how to easily connect different URLs to their associated functions.
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When a client requests a specific URL from the HTTP server,
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it divides it into several parts (CGI variables): `SCRIPT_NAME`, `PATH_INFO` and `QUERY_STRING`. For example
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the URL `/foo/bar.php/test?x=10` is separated into:
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- `SCRIPT_NAME` = `/foo/bar.php`
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- `PATH_INFO` = `/test`
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- `QUERY_STRING` = `x=10`
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CppCMS web applications are not distributed into several
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scripts, but rather they're written using a single FastCGI application that runs on a specific "script" url, like "/myapp". So generally URLs would look like `/myapp/page/10`, where
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`SCRIPT_NAME` = "/myapp" would remain constant and `PATH_INFO` = `/page/10` is changed according to the user's needs.
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So the mapping between the URL and the application's member functions is done by matching a regular expression against the `PATH_INFO` part of the URL, even though this behaviour can be changed by using the `mount_point` class.
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This job is done by the `cppcms::url_dispatcher` class.
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The opposite of dispatching is "mapping", where the names of the application parts are converted to URLs that can be given to the user.
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## Code
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### Mapping
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Lets rewrite our [hello class](/wikipp/en/page/cppcms_1x_tut_hello):
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Since we will be routing URLs, let's include the `url_dispatcher.h` and `url_mapper.h` header file. Your include list should look like:
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#include <cppcms/application.h>
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#include <cppcms/service.h>
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#include <cppcms/http_response.h>
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#include <cppcms/url_dispatcher.h>
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#include <cppcms/url_mapper.h>
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#include <cppcms/applications_pool.h>
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#include <iostream>
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#include <stdlib.h>
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Now in our constructor, let's map some URLs to member functions:
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hello(cppcms::service &srv) :
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cppcms::application(srv)
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{
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dispatcher().assign("/number/(\\d+)",&hello::number,this,1);
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mapper().assign("number","/number/{1}");
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dispatcher().assign("/smile",&hello::smile,this);
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mapper().assign("smile","/smile");
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dispatcher().assign("",&hello::welcome,this);
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mapper().assign("");
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mapper().root("/hello");
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}
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In the fourth line we connect the regular expression `/number/(\d+)` to the member function `number` of `this`
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instance that receives `std::string` as parameter,
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and the 1st captured subexpression is passed to it (note the parameter 1 that represents the 1st subexpression as a parameter)
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In this case the subexpression is a nonempty string that contains digits.
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In the 5th line we create a name for this part called
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"number" and we provide an URL formatting pattern of `/number/{1}` - the opposite of the regular expression where `{1}` is a placeholder for the first parameter for formatting the appropriate URL.
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In the lines 7-8 we connect the member function `smile`
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to its URL and create a mapping. Because this URL
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does not have any parameters it does not have
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any placeholders.
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On line 10 we connect the empty URL to the
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`welcome` member function, and on line 11 we define the default empty mapping pattern for the URL. Note, because
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we pass only one parameter to the `assign()` function,
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we define the default URL for the application.
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On line 13 we define the "root" of all the URLs for the
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`url_mapper` class, in our case it should be identical to
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the `SCRIPT_NAME` CGI variable.
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### Description
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So when the web server receives requests that match
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a script name `/hello` it forwards them to the application:
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- `/hello` - `welcome` function would be called
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- `/hello/smile` - `smile` function would be called
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- `/hello/number/10` - `number` function would be called and receive a string "10" as a parameter.
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Because the "routing table" between the URL and the
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application's member functions is done, we don't need
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to override the `cppcms::application::main` member
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function as it does all the dispatching for us.
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### Actions
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The "number" member function.
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void number(std::string num)
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{
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int no = atoi(num.c_str());
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response().out() << "The number is " << no << "<br/>\n";
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response().out() << "<a href='" << url("/") << "'>Go back</a>";
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}
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Note, we're using `url("/")` as an abstract URL for the default application entry point - the `/` part describes the root application (our single application) and the fact that nothing follows it shows that the default URL should be
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given - the mapping to the `welcome` member function.
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In the same way we create the `smile` member function:
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void smile()
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{
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response().out() << ":-) <br/>\n";
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response().out() << "<a href='" << url("/") << "'>Go back</a>";
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}
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Now we write out the `welcome` action:
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void welcome()
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{
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response().out() <<
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"<h1> Welcome To Page with links </h1>\n"
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"<a href='" << url("/number",1) << "'>1</a><br>\n"
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"<a href='" << url("/number",15) << "'>15</a><br>\n"
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"<a href='" << url("/smile") << "' >:-)</a><br>\n";
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}
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Note, we show three URLs to the different application
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parts: "number" - and we pass a parameter `1` to the `cppcms::application::url` function that will be rendered instead of the placeholder `{1}`, we do the same for
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number 15 and pass an URL to "smile" without parameters.
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Lets describe the actions that are taken in the example when we call `url("/number",15)`:
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- First for "/" we go to the topmost application, in out case to `this` one.
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- Next we match "number" against the known pattern "number" that was mapped to `"/number/{1}"`.
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- We fetch the pattern and use the parameter that is passed to `url` function and convert: `/number/{1}` to `/number/15`.
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- Finally we prepend the root URL path "/hello" and get our final URL `/hello/number/15`.
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Note: the parameters to `url` family of functions can be anything that can be written to `std::ostream` - i.e. any object that defines operator `<<` with standard C++ streams.
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## Running The Example
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Recompile it:
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c++ hello.cpp -lcppcms -o hello
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And now for the exciting part, start your application:
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./hello -c config.js
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And hit the URL: <http://localhost:8080/hello> |
And hit the URL: <http://localhost:8080/hello>
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---
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← [Using Templates (v 1.x)][prev]
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| [Top](#maincontent)
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| [Applications Hierarchy][next] →
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[prev]: /wikipp/en/page/cppcms_1x_tut_hello_templates
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[next]: /wikipp/en/page/cppcms_1x_tut_hierarchy |
