ecpp 7 2006-07-23 Tntnet Tntnet users guide


ecpp - template language for tntnet(8)


ecpp is the template language used by the tntnet system to generate dynamic content.

A template consists of normal content (normally html data) enriched with special tags, which trigger some special handling.

One ecpp file is compiled into a C++ class. The C++ class is placed into the namespace component. A ecpp file compiled into a C++ class is called component. The name of the class is the basename of the file.

request, reply, qparam

Each component has 3 parameters: request, reply and qparam. request holds information about the client request like http headers and the url, but also additional parameters specified in the config file tntnet.xml(7). The type of request is tnt::HttpRequest.

reply receives the answer from the component. The component can set additional http headers here, set cookies and - most important - generate output. The most important methods here are reply.out() and reply.sout(). Both return a std::ostream, which receives the output of the component. reply.sout() has a filter installed, which translates some characters, with special meanings in html to the corresponding html entities. The characters are <, >, &, " and '. This is useful for printing values from variables to the html code.

qparam holds the query parameters parsed from GET- or POST-parameters or received from other components. The type of qparam is tnt::QueryParams. Normally you use a <%args> block to specify the parameters, but there are special cases, where it is useful to access these directly.

component addressing

Each component has a unique name. The name is composed from the class name, the character '@' and the name of the shared library, it is located. Components can have internal sub components. The name of the internal sub component is appended to the class name separated by a dot (.).

special rule for line feeds after a </%something>-tag

A line feed immediately after a closing tag for all <%something> blocks are ignored. Hence blocks followed immediately one after another does not generate white space in output, which is often undesirable.


Error handling is done by exception. Tntnet catches all exceptions thrown by components and handles them properly. Exceptions must be derived from std::exception. Exceptions derived from tnt::HttpError, are handled separately. They carry a http return code, which is sent to the client. Other exceptions derived from std::exception, result in a http error code 500 (Internal Server Error).


<$ expr $>
Print expressions expr to the output stream. The characters <, >, &, " and ', which have special meanings in html, are translated to the corresponding html entities.
<$$ expr $>
Print expressions expr without translating characters with special meaning in html to html entities to the output stream.
<? cond ? expr ?>
Conditional output. Print expression expr to the output stream, if cond evaluates to true. Characters with special meaning in html are translated to the corresponding html entities.
<?? cond ? expr ?>
Conditional output. Print expression expr to the output stream, if cond evaluates to true. Characters with special meaning in html are not translated to the corresponding html entities.
<& component [ arguments ] >
Call the specified component. The output of the component is printed into the output stream. If the component name does not start with a letter, the ecpp compiler treats it as a expression, which returns the name of the component. You must surround the expression in brackets, if it contains spaces.
The arguments part specify the parameters, the component will receive. Arguments are name value pairs separated by '='. They are put in the qparam parameter of the component and are normally declared in the <%args> block. Values can be specified in 3 forms:
As a plain word without spaces
As a string enclosed in quotation marks
As a expression enclosed in brackets
A single plain word in the argument list is treated as a variable of type cxxtools::QueryParams and a copy is passed to the component. Other parameters are added to this copy. If you want to pass all parameters of the current component put the variable qparam as a plain word in the argument list.
Closing tag for a component call. When components are called, this closing tag might occur later. The code in <%close> block is placed here.
C++ inline processing block. The code in this block is copied into the C++ class unchanged.
A linefeed after the closing tag is not ignored.
Comment block. Everything in this block is ignored.
<%application [ scope="component|page|shared|global" ] >...</%application>
Variables defined here, have the lifetime of the application.
Application scope is automatically locked.
Defines GET or POST parameters received by the component.
Each argument has a name and optionally a default value. The default value is delimited by '=' from the name. A single argument definition followed by a semicolon (;). In the component a variable with the same name of type std::string is defined, which receives the value.
A argument name can be prefixed by a type definition. The ecpp compiler generates code, which tries to convert the value with the cxxtools deserialization operator. If the argument can't be converted, the default value is set.
Argument names can be postfixed by empty square brackets. This defines a std::vector with the specified type or std::string, if no type is specified. This way multiple values with the same name can be received. If a type is specified, each value is converted to the target type.
Components may define attributes, which can be queried from other components. These values are strings and are defined by specifying a name followed by '=' and the string value. No type is allowed here.
A other component can the fetch a reference to the component using fetchComp(name). fetchComp is a member of the base class tnt::EcppComponent of components built with ecpp.
The component has then a member method getAttribute(name), which returns the attribute or a empty string when not found. A different default string can be passed as a second parameter to getAttribute.


A content component specifies a title:
title = "my title";
A component webmain want to add a title depending on a content component:
    <$ fetchComp("theContent").getAttribute("title", "default title") $>
To separte the C++ code from the html, the actual doing can be moved to a C++ section. The component can then be also called later to generate the content:
  tnt::Component& theContent = fetchComp("theContent");
  std::string title = theContent.getAttribute("title", "default title");
  <title><$ title $></title>
  <div id="contnent">
    <{ theContent(request, reply, qparam); }>
Code in these tags is placed into the calling component, when a closing tag </&component> is found.
The <%close> receives the same parameters like the corresponding normal component call.
This tag is deprecated and should not be used any more.
Often web applications need some configuration like database names or login information to the database. These configuration variables can be read from the tntnet.xml. Variable names ended with a semicolon are defined as static std::string variables and filled from tntnet.xml. A variable can be prepended by a type. The value from tntnet.xml is then converted with a std::istream.
You can also specify a default value by appending a '=' and the value to the variable.


  dburl = "sqlite:db=mydbfile.sqlite";
  int maxvalue = 10;
C++ processing block. The code between these tags are copied into the C++ class unchanged.
A linefeed after the closing tag is ignored.
<%def name>...</%def>
Defines a internal sub component with the name name, which can be called like other components.
Comment block. Everything in this block is ignored.
A linefeed after the closing tag is ignored.
Works like a <%args> block but receives only GET parameters.
The specified file is read and compiled.
Defines parameter received from calling components. In contrast to query parameters these variables can be of any type. The syntax (and the underlying technology) is the same like in scoped variables. See the description about scoped variables to see how to define parameters. The main difference is, that a parameter variable has no scope, since the parameter is always local to the component.
<%out> expr </%out>
Same as <$$ ... $>. Prints the contained C++ expression expr.
Works like a <%args> block but receives only POST parameters.
Defines C++ code, which is placed outside the C++ class and outside the namespace definition. This is a good place to define #include directives.
<%request [ scope="component|page|shared|global" ] >...</%request>
Define request scope variables. Variables defined here, has the lifetime of the request.
<%session [ scope="component|page|shared|global" ] >...</%session>
Variables defined here, has the lifetime of the session.
Sessions are identified with cookies. If a <%session> block is defined somewhere in a component, a session cookie is sent to the client.
Sessions are automatically locked.
<%securesession [ scope="component|page|shared|global" ] >...</%securesession>
Secure session is just like session but a secure cookie is used to identify the session. Secure cookies are transferred only over a ssl connection from the browser and hence the variables are only kept in a ssl secured application.
If a variable defined here is used in a non ssl page, the variable values are lost after the current request.
<%sout> expr </%sout>
Same as <$ ... $>. Prints the contained C++ expression expr. The characters <, >, &, " and ', which have special meanings in html, are translated to the corresponding html entities.
<%thread [ scope="component|page|shared|global" ] >...</%thread>
Variables defined here, has the lifetime of the thread. Each thread has his own instance of these variables.
Thread scope variables do not need to be locked at all, because they are only valid in the current thread.


Scoped variables are c++ variables, whose lifetime is handled by tntnet. These variables has a lifetime and a scope. The lifetime is defined by the tag, used to declare the variable and the scope is passed as a parameter to the tag.

There are 5 different lifetimes for scoped variables:

The variable is valid in the current request. The tag is <%request>.
The variable is valid in the application. The tag is <%application>. The application is specified by the shared library of the top level component.
The variable is valid for the current session. The tag is <%session>. If at least session variable is declared in the current request, a session cookie is sent to the client.
The variable is valid in the current thread. The tag is <%thread>.
The variable receives parameters. The tag is <%param>.

And 3 scopes:

The variable is only valid in the same component. This is the default scope.
The variable is shared between the components in a single ecpp file. You can specify multiple internal sub components in a <%def> block. Variables, defined in page scope are shared between these sub components.
global or shared
Variables are shared between all components. If you define the same variable with shared scope in different components, they must have the same type. This is achieved most easily defining them in a separate file and include them with a <%include> block. The global and shared are just synonyms.
Variables are automatically locked as needed. If you use session variables, tntnet ensures, that all requests of the same session are serialized. If you use application variables, tntnet serializes all requests to the same application scope. Request and thread scope variables do not need to be locked at all, because they are not shared between threads.

Syntax of scoped variables

Scoped variables are declared with exactly the same syntax as normal variables in c++ code. They can be of any type and are instantiated, when needed. Objects, which do not have default constructors, need to be specified with proper constructor parameters in brackets or separated by '='. The parameters are only used, if the variable need to be instantiated. This means, that parameters to e.g. application scope variables are only used once. When the same component is called later in the same or another request, the parameters are not used any more.


Specify a application specific shared variable, which is initialized with 0:

unsigned count = 0;

Specify a variable with a user defined type, which holds the state of the session:

MyClass sessionState;

Specify a persistent database connection, which is initialized, when first needed and hold for the lifetime of the current thread. This variable may be used in other components:

<%thread scope="shared">
tntdb::Connection conn(dburl);


This manual page was written by Tommi Mäkitalo


tntnet(8), ecppc(1)