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Version: v20 R4

Balises de transformation

4D fournit un ensemble de balises de transformation qui vous permettent d'insérer des références à des variables ou des expressions 4D, ou d'effectuer différents types de traitement dans un texte source, appelé "template". Ces balises sont interprétées lors de l'exécution du texte source et génèrent un texte de sortie.

This principle is used in particular by the 4D Web server to build web template pages.

These tags are generally to be inserted as HTML type comments (<!--#Tag Contents-->) but an xml-compliant alternative syntax is available for some of them.

Il est possible de combiner plusieurs types de balises. Par exemple, la structure HTML suivante est tout à fait envisageable :

<HTML>
<BODY>
<!--#4DSCRIPT/PRE_PROCESS-->   (Method call)
<!--#4DIF (myvar=1)-->   (If condition)
   <!--#4DINCLUDE banner1.html-->   (Subpage insertion)
<!--#4DENDIF-->   (End if)
<!--#4DIF (mtvar=2)-->
   <!--#4DINCLUDE banner2.html-->
<!--#4DENDIF-->

<!--#4DLOOP [TABLE]-->   (Loop on the current selection)
<!--#4DIF ([TABLE]ValNum>10)-->   (If [TABLE]ValNum>10)
   <!--#4DINCLUDE subpage.html-->   (Subpage insertion)
<!--#4DELSE-->   (Else)
   <B>Value: <!--#4DTEXT [TABLE]ValNum--></B><br/>   (Field display)
<!--#4DENDIF-->
<!--#4DENDLOOP-->   ](End for)
</BODY>
</HTML>

Principes d'utilisation des balises​

Parsing​

Parsing the contents of a template source is done in two contexts:

  • Using the PROCESS 4D TAGS command; this command accepts a template as input, as well as optional parameters and returns a text resulting from the processing.

  • Using 4D's integrated HTTP server: template pages sent by means of the WEB SEND FILE (.htm, .html, .shtm, .shtml), WEB SEND BLOB (text/html type BLOB), WEB SEND TEXT commands, or called using URLs. Dans ce dernier cas, à des fins d'optimisation, les pages suffixées par ".htm" et ".html" ne sont PAS parsées. In order to parse HTML pages in this case, you must add the suffix “.shtm” or “.shtml” (for example, http\://www.server.com/dir/page.shtm).

Traitement récursif​

Les balises 4D sont interprétées de manière récursive : 4D tente toujours de réinterpréter le résultat d'une transformation et, si une nouvelle transformation a eu lieu, une interprétation supplémentaire est effectuée, et ainsi de suite jusqu'à ce que le produit obtenu ne nécessite plus aucune transformation. Par exemple, étant donné l'énoncé suivant :

<!--#4DHTML [Mail]Letter_type-->

If the [Mail]Letter_type text field itself contains a tag, for example <!--#4DSCRIPT/m_Gender-->, this tag will be evaluated recursively after the interpretation of the 4DHTML tag.

Ce principe puissant répond à la plupart des besoins liés à la transformation des textes. Note, however, that in some cases this can also allow malicious code to be inserted in the web context, which can be avoided.

Identifiants avec tokens​

Pour garantir l'évaluation correcte des expressions traitées via les balises, quel que soit le langage ou la version de 4D, il est recommandé d'utiliser la syntaxe tokenisée pour les éléments dont le nom peut varier selon les versions (commandes, tables, champs, constantes). For example, to insert the Current time command, enter Current time:C178.

Utilisation du "." comme séparateur décimal​

4D always uses the period character (.) as a decimal separator when evaluating a numerical expression using a 4D tag 4DTEXT, 4DHTML, and 4DEVAL. Les paramètres régionaux sont ignorés. Cette fonctionnalité facilite la maintenance du code et la compatibilité entre les langues et les versions de 4D.

4DBASE​

Syntax: <!--#4DBASE folderPath-->​

The <!--#4DBASE --> tag designates the working directory to be used by the <!--#4DINCLUDE--> tag.

When it is called in a Web page, the <!--#4DBASE --> tag modifies all subsequent <!--#4DINCLUDE--> calls on this page, until the next <!--........-->, if any. If the<!--#4DBASE --> folder is modified from within an included file, it retrieves its original value from the parent file.

The folderPath parameter must contain a pathname relative to the current page and it must end with a slash (/). Le dossier désigné doit être situé à l'intérieur du dossier Web.

Passez le mot-clé "WEBFOLDER" pour rétablir le chemin par défaut (relatif à la page).

Le code suivant, qui doit spécifier un chemin relatif pour chaque appel :

<!--#4DINCLUDE subpage.html-->
<!--#4DINCLUDE folder/subpage1.html-->
<!--#4DINCLUDE folder/subpage2.html-->
<!--#4DINCLUDE folder/subpage3.html-->
<!--#4DINCLUDE ../folder/subpage.html-->

... is equivalent to:

<!--#4DINCLUDE subpage.html-->
<!--#4DBASE folder/-->
<!--#4DINCLUDE subpage1.html-->
<!--#4DINCLUDE subpage2.html-->
<!--#4DINCLUDE subpage3.html-->
<!--#4DBASE ../folder/-->
<!--#4DINCLUDE subpage.html-->
<!--#4DBASE WEBFOLDER-->

Par exemple, pour définir un répertoire pour la page d'accueil :

/* Index.html */
<!--#4DIF LangFR=True-->
    <!--#4DBASE FR/-->
<!--#4DELSE-->
    <!--#4DBASE US/-->
<!--#4DENDIF-->
<!--#4DINCLUDE head.html-->
<!--#4DINCLUDE body.html-->
<!--#4DINCLUDE footer.html-->

In the "head.html" file, the current folder is modified through <!--#4DBASE -->, without this changing its value in "Index.html":

/* Head.htm */
/* the working directory here is relative to the included file (FR/ or US/) */
<!--#4DBASE Styles/-->
<!--#4DINCLUDE main.css-->
<!--#4DINCLUDE product.css-->
<!--#4DBASE Scripts/-->
<!--#4DINCLUDE main.js-->
<!--#4DINCLUDE product.js-->

4DCODE​

Syntax: <!--#4DCODE codeLines-->​

The 4DCODE tag allows you to insert a multi-line 4D code block in a template.

When a <!--#4DCODE sequence is detected that is followed by a space, a CR or a LF character, 4D interprets all the lines of code up to the next --> sequence. Le bloc de code lui-même peut contenir des retours chariot, des sauts de ligne ou les deux ; il sera interprété séquentiellement par 4D.

Par exemple, vous pouvez écrire dans un template :

<!--#4DCODE
//PARAMETERS initialization
C_OBJECT:C1216($graphParameters)
OB SET:C1220($graphParameters;"graphType";1)
$graphType:=1
//...your code here
If(OB Is defined:C1231($graphParameters;"graphType"))
    $graphType:=OB GET:C1224($graphParameters;"graphType")
    If($graphType=7)
        $nbSeries:=1
        If($nbValues>8)
            DELETE FROM ARRAY:C228 ($yValuesArrPtr{1}->;9;100000)
            $nbValues:=8
        End if
    End if
End if
-->

Voici les caractéristiques de la balise 4DCODE :

  • The TRACE command is supported and activates the 4D debugger, thus allowing you to debug your template code.
  • Toute erreur affichera le dialogue d'erreur standard qui permet à l'utilisateur d'arrêter l'exécution du code ou d'entrer en mode débogage.
  • The text in between <!--#4DCODE and --> is split into lines accepting any line-ending convention (cr, lf, or crlf).
  • The text is tokenized within the context of the database that called PROCESS 4D TAGS. Ceci est important pour la reconnaissance des méthodes de projet par exemple. The Available through tags and 4D URLs (4DACTION ...) method property is not taken into account.
  • Même si le texte utilise toujours l'anglais-US, il est recommandé d'utiliser la syntaxe token (:Cxxx) pour les noms de commandes et de constantes afin de se prémunir contre d'éventuels problèmes dus à des commandes ou des constantes renommées d'une version de 4D à une autre.

Le fait que les balises 4DCODE puissent appeler n'importe quelle commande du langage 4D ou méthode du projet pourrait être considéré comme un problème de sécurité, en particulier lorsque la base de données est disponible via HTTP. Toutefois, étant donné qu'elle exécute du code côté serveur appelé à partir de vos propres fichiers de modèle, la balise elle-même ne représente pas un problème de sécurité. Dans ce contexte, comme pour tout serveur Web, la sécurité est principalement gérée au niveau des accès distants aux fichiers du serveur.

4DEACH et 4DENDEACH​

Syntax: <!--#4DEACH variable in expression--> <!--#4DENDEACH-->​

The <!--#4DEACH--> comment allows iterating a specified item over all values of the expression. The item is set to a variable whose type depends on the expression type.

The <!--#4DEACH--> comment can iterate through three expression types:

Le nombre d'itérations est évalué au démarrage et ne changera pas pendant le traitement. L'ajout ou la suppression d'éléments pendant la boucle est donc déconseillé car il pourra en résulter une redondance ou un manque d'itérations.

<!--#4DEACH item in collection-->​

This syntax iterates on each item of the collection. The code portion located between <!--#4DEACH --> and <!--#4DENDEACH--> is repeated for each collection element.

The item parameter is a variable of the same type as the collection elements.

The collection must contain only elements of the same type, otherwise an error is returned as soon as the item variable is assigned the first mismatched value type.

Le nombre de boucles est basé sur le nombre d'éléments de la collection. At each iteration, the item variable is automatically filled with the matching element of the collection. Vous devez tenir compte des points suivants :

  • If the item variable is of the object type or collection type (i.e. if expression is a collection of objects or of collections), modifying this variable will automatically modify the matching element of the collection (because objects and collections share the same references). If any collection item is not of the same type as the variable, an error is generated and the loop stops.
  • The item variable gets the same type as the first collection element. If any collection item is not of the same type as the variable, an error is generated and the loop stops.
  • If the collection contains elements with a Null value, an error is generated if the item variable type does not support Null values (such as longint variables).

Exemple avec une collection de valeurs scalaires​

getNames returns a collection of strings. The method has been declared as "available through 4D tags and URLs".

 <table class="table">    

        <tr><th>Name</th></tr>

          <!--#4DEACH $name in getNames-->
        <tr>
            <td><!--#4DTEXT $name--></td>
        </tr>
          <!--#4DENDEACH-->
    </table>

Exemple avec une collection d'objets​

getSalesPersons returns a collection of objects.

    <table class="table">    
         <!--#4DCODE
            $salePersons:=getSalesPersons
          -->          
       <tr><th>ID</th><th>Firstname</th><th>Lastname</th></tr>

          <!--#4DEACH $salesPerson in $salePersons-->
        <tr>
            <td><!--#4DTEXT $salesPerson.ID--></td>
            <td><!--#4DTEXT $salesPerson.firstname--></td>
            <td><!--#4DTEXT $salesPerson.lastname--></td>
        </tr>
          <!--#4DENDEACH-->
    </table>

<!--#4DEACH entity in entitySelection-->​

This syntax iterates on each entity of the entitySelection. The code portion located between <!--#4DEACH --> and <!--#4DENDEACH--> is repeated for each entity of the entity selection.

The entity parameter is an object variable of the entity selection class.

Le nombre de boucles est basé sur le nombre d'entities présentes dans l'entity selection. At each iteration, the entity object variable is automatically filled with the matching entity of the entity selection.

Exemple avec un tableau html​

    <table class="table">     

        <tr><th>ID</th><th>Name</th><th>Total purchase</th></tr>

          <!--#4DEACH $customer in ds.Customers.all()-->
        <tr>
            <td><!--#4DTEXT $customer.ID--></td>
            <td><!--#4DTEXT $customer.name--></td>
            <td><center><!--#4DTEXT String($customer.totalPurchase;"$###,##0")--></center></td>
        </tr>
          <!--#4DENDEACH-->
    </table>

Example with PROCESS 4D TAGS​

var customers : cs.CustomersSelection
var $input; $output : Text

customers:=ds.Customers.all()
$input:="<!--#4DEACH $cust in customers-->"
$input:=$input+"<!--#4DTEXT $cust.name -->"+Char(Carriage return)
$input:=$input+"<!--#4DENDEACH-->"
PROCESS 4D TAGS($input; $output)
TEXT TO DOCUMENT("customers.txt"; $output)

<!--#4DEACH property in object-->​

This syntax iterates on each property of the object. The code portion located between <!--#4DEACH --> and <!--#4DENDEACH--> is repeated for each property of the object.

The property parameter is a text variable automatically filled with the name of the currently processed property.

The properties of the object are processed according to their creation order. Pendant la boucle, il est possible d'ajouter ou de supprimer des propriétés dans l'objet, sans pour autant modifier le nombre de boucles qui reste basé sur le nombre de propriétés initial de l'objet.

Example with the properties of an object​

getGamers is a project method that returns an object like ("Mary"; 10; "Ann"; 20; "John"; 40) to figure gamer scores.

    <table class="table">    
          <!--#4DCODE
           $gamers:=getGamers
          -->          

        <tr><th>Gamers</th><th>Scores</th></tr>

          <!--#4DEACH $key in $gamers-->
        <tr>
            <td ><!--#4DTEXT $key--></td>
            <td ><!--#4DTEXT $gamers[$key]--></td>
        </tr>
          <!--#4DENDEACH-->
    </table>

4DEVAL​

Syntax: <!--#4DEVAL expression-->​

Alternative syntax: $4DEVAL(expression)​

The 4DEVAL tag allows you to assess a 4D variable or expression. Like the 4DHTML tag, 4DEVAL does not escape HTML characters when returning text. However, unlike 4DHTML or 4DTEXT, 4DEVAL allows you to execute any valid 4D statement, including assignments and expressions that do not return any value.

For example, you can execute:

 $input:="<!--#4DEVAL a:=42-->" //assignment
 $input:=$input+"<!--#4DEVAL a+1-->" //calculation
 PROCESS 4D TAGS($input;$output)
  //$output = "43"

In case of an error during interpretation, the text inserted will be in the form: <!--#4DEVAL expr-->: ## error # error code.

For security reasons, it is recommended to use the 4DTEXT tag when processing data introduced from outside the application, in order to prevent the insertion of malicious code.

4DHTML​

Syntax: <!--#4DHTML expression-->​

Alternative syntax: $4DHTML(expression)​

Just like the 4DTEXT tag, this tag lets you assess a 4D variable or expression that returns a value, and insert it as an HTML expression. Unlike the 4DTEXT tag, this tag does not escape HTML special characters (e.g. ">").

For example, here are the processing results of the 4D text variable myvar with the available tags:

myvar ValueTagsRésultat
myvar:="<B>"<!--#4DTEXT myvar-->&amp;lt;B&amp;gt;
myvar:="<B>"<!--#4DHTML myvar--><B>

In case of an interpretation error, the inserted text will be <!--#4DHTML myvar--> : ## error # error code.

For security reasons, it is recommended to use the 4DTEXT tag when processing data introduced from outside the application, in order to prevent the insertion of malicious code.

4DIF, 4DELSE, 4DELSEIF et 4DENDIF​

Syntax: <!--#4DIF expression--> {<!--#4DELSEIF expression2-->...<!--#4DELSEIF expressionN-->} {<!--#4DELSE-->} <!--#4DENDIF-->​

Used with the <!--#4DELSEIF--> (optional), <!--#4DELSE--> (optional) and <!--#4DENDIF--> comments, the <!--#4DIF expression--> comment offers the possibility to execute portions of code conditionally.

The expression parameter can contain any valid 4D expression returning a Boolean value. It must be indicated within parenthesis and comply with the 4D syntax rules.

The <!--#4DIF expression--> ... <!--#4DENDIF--> blocks can be nested in several levels. Like in 4D, each <!--#4DIF expression--> must match a <!--#4DENDIF-->.

In case of an interpretation error, the text "<!--#4DIF expression-->: A Boolean expression was expected" is inserted instead of the contents located between <!--#4DIF --> and <!--#4DENDIF-->. Likewise, if there are not as many <!--#4DENDIF--> as <!--#4DIF -->, the text "<!--#4DIF expression-->: 4DENDIF expected" is inserted instead of the contents located between <!--#4DIF --> and <!--#4DENDIF-->.

Using the <!--#4DELSEIF--> tag, you can test an unlimited number of conditions. Only the code that follows the first condition evaluated as True is executed. If no conditions are true, no statement is executed (if there is no final <!--#4DELSE-->). You can use a <!--#4DELSE--> tag after the last <!--#4DELSEIF-->. If all the conditions are false, the statements following the <!--#4DELSE--> are executed.

The two following codes are equivalent.

Code using 4DELSE only:

<!--#4DIF Condition1-->
  /* Condition1 is true*/
<!--#4DELSE-->
    <!--#4DIF Condition2-->
        /* Condition2 is true*/
    <!--#4DELSE-->
        <!--#4DIF Condition3-->
            /* Condition3 is true */
        <!--#4DELSE-->
            /*None of the conditions are true*/
        <!--#4DENDIF-->
    <!--#4DENDIF-->
<!--#4DENDIF-->

Similar code using the 4DELSEIF tag:

<!--#4DIF Condition1-->
     /* Condition1 is true*/
<!--#4DELSEIF Condition2-->
     /* Condition2 is true*/
<!--#4DELSEIF Condition3-->
    /* Condition3 is true */
<!--#4DELSE-->
    /* None of the conditions are true*/
<!--#4DENDIF-->

This example of code inserted in a static HTML page displays a different label according the vname#"" expression result:

<BODY>
...
<!--#4DIF (vname#"")-->
Names starting with <!--#4DTEXT vname-->.
<!--#4DELSE-->
No name has been found.
<!--#4DENDIF-->
...
</BODY>

This example inserts different pages depending on which user is connected:

<!--#4DIF LoggedIn=False-->
    <!--#4DINCLUDE Login.htm -->
<!--#4DELSEIF User="Admin" -->
    <!--#4DINCLUDE AdminPanel.htm -->
<!--#4DELSEIF User="Manager" -->
    <!--#4DINCLUDE SalesDashboard.htm -->
<!--#4DELSE-->
    <!--#4DINCLUDE ItemList.htm -->
<!--#4DENDIF-->

4DINCLUDE​

Syntax: <!--#4DINCLUDE path-->​

This tag is mainly designed to include an HTML page (indicated by the path parameter) in another HTML page. By default, only the body of the specified HTML page, i.e. the contents found within the <body> and </body> tags, is included (the tags themselves are not included). This lets you avoid conflicts related to meta tags present in the headers.

However, if the HTML page specified does not contain <body>``</body> tags, the entire page is included. It is up to you to verify the consistency of the meta tags.

The <!--#4DINCLUDE --> comment is very useful for tests (<!--#4DIF-->) or loops (<!--#4DLOOP-->). It is very convenient to include banners according to a criteria or randomly. When including, regardless of the file name extension, 4D analyzes the called page and then inserts the contents (modified or not) in the page originating the 4DINCLUDE call.

An included page with the <!--#4DINCLUDE --> comment is loaded in the Web server cache the same way as pages called via a URL or sent with the WEB SEND FILE command.

In path, put the path leading to the document to include. Warning: In the case of a 4DINCLUDE call, the path is relative to the document being analyzed, that is, the "parent" document. Use the slash character (/) as a folder separator and the two dots (..) to go up one level (HTML syntax). When you use the 4DINCLUDE tag with the PROCESS 4D TAGS command, the default folder is the project folder.

You can modify the default folder used by the 4DINCLUDE tag in the current page, using the <!--#4DBASE --> tag (see below).

The number of <!--#4DINCLUDE path--> within a page is unlimited. However, the <!--#4DINCLUDE path--> calls can be made only at one level. This means that, for example, you cannot insert <!--#4DINCLUDE mydoc3.html--> in the mydoc2.html body page, which is called by <!--#4DINCLUDE mydoc2--> inserted in mydoc1.html. Furthermore, 4D verifies that inclusions are not recursive.

In case of error, the inserted text is "<!--#4DINCLUDE path--> :The document cannot be opened".

Exemples :

<!--#4DINCLUDE subpage.html-->
<!--#4DINCLUDE folder/subpage.html-->
<!--#4DINCLUDE ../folder/subpage.html-->

4DLOOP et 4DENDLOOP​

Syntax: <!--#4DLOOP condition--> <!--#4DENDLOOP-->​

This comment allows repetition of a portion of code as long as the condition is fulfilled. The portion is delimited by <!--#4DLOOP--> and <!--#4DENDLOOP-->.

The <!--#4DLOOP condition--> ... <!--#4DENDLOOP--> blocks can be nested. Like in 4D, each <!--#4DLOOP condition--> must match a <!--#4DENDLOOP-->.

There are five kinds of conditions:

<!--#4DLOOP [table]-->​

This syntax makes a loop for each record from the table current selection in the current process. The code portion located between the two comments is repeated for each current selection record.

When the 4DLOOP tag is used with a table, records are loaded in "Read only" mode.

Le code suivant :

<!--#4DLOOP [People]-->
<!--#4DTEXT [People]Name--> <!--#4DTEXT [People]Surname--><br/>
<!--#4DENDLOOP-->

... could be expressed in 4D language in the following way:

 FIRST RECORD([People])
 While(Not(End selec tion([People])))
    ...
    NEXT RECORD([People])
 End while

<!--#4DLOOP array-->​

This syntax makes a loop for each array item. The array current item is increased when each code portion is repeated.

This syntax cannot be used with two dimension arrays. In this case, it is better to combine a method with nested loops.

The following code example:

<!--#4DLOOP arr_names-->
<!--#4DTEXT arr_names{arr_names}--><br/>
<!--#4DENDLOOP-->

... could be expressed in 4D language in the following way:

 For($Elem;1;Size of array(arr_names))
    arr_names:=$Elem
    ...
 End for

<!--#4DLOOP method-->​

This syntax makes a loop as long as the method returns True. The method takes a Long Integer parameter type. First it is called with the value 0 to allow an initialization stage (if necessary); it is then called with the values 1 ,then 2, then 3 and so on, as long as it returns True.

For security reasons, within a Web process, the On Web Authentication database method can be called once just before the initialization stage (method execution with 0 as parameter). If the authentication is OK, the initialization stage will proceed.

C_BOOLEAN($0) and C_LONGINT($1) MUST be declared within the method for compilation purposes.

The following code example:

<!--#4DLOOP my_method-->
<!--#4DTEXT var--> <br/>
<!--#4DENDLOOP-->

... could be expressed in 4D language in the following way:

 If(AuthenticationWebOK)
    If(my_method(0))
       $counter:=1
       While(my_method($counter))
          ...
          $counter:=$counter+1
       End while
    End if
 End if

The my_method method can be as follows:

 C_LONGINT($1)
 C_BOOLEAN($0)
 If($1=0) `Initialisation
    $0:=True
 Else
    If($1<50)
       ...
       var:=...
       $0:=True
    Else
       $0:=False `Stops the loop
    End if
 End if

<!--#4DLOOP expression-->​

With this syntax, the 4DLOOP tag makes a loop as long as the expression returns True. The expression can be any valid Boolean expression and must contain a variable part to be evaluated in each loop to avoid infinite loops.

For example, the following code:

<!--#4DEVAL $i:=0-->
<!--#4DLOOP ($i<4)-->
<!--#4DEVAL $i-->
<!--#4DEVAL $i:=$i+1-->
<!--#4DENDLOOP-->

...produces the following result:


0

1
2
3

<!--#4DLOOP pointerArray-->​

In this case, the 4DLOOP tag works like it does with an array: it makes a loop for each element of the array referenced by the pointer. The current array element is increased each time the portion of code is repeated.

This syntax is useful when you pass an array pointer as a parameter to the PROCESS 4D TAGS command.

Voici un exemple :

 ARRAY TEXT($array;2)
 $array{1}:="hello"
 $array{2}:="world"
 $input:="<!--#4DEVAL $1-->"
 $input:=$input+"<!--#4DLOOP $2-->"
 $input:=$input+"<!--#4DEVAL $2->{$2->}--> "
 $input:=$input+"<!--#4DENDLOOP-->"
 PROCESS 4D TAGS($input;$output;"elements = ";->$array)
  // $output = "elements = hello world "

In case of an interpretation error, the text "<!--#4DLOOP expression-->: description" is inserted instead of the contents located between <!--#4DLOOP --> and <!--#4DENDLOOP-->.

The following messages can be displayed:

  • Unexpected expression type (standard error);
  • Incorrect table name (error on the table name);
  • An array was expected (the variable is not an array or is a two dimension array);
  • The method does not exist;
  • Syntax error (when the method is executing);
  • Access error (you do not have the appropriate access privileges to access the table or the method).
  • 4DENDLOOP expected (the <!--#4DENDLOOP--> number does not match the <!--#4DLOOP -->).

4DSCRIPT/​

Syntax: <!--#4DSCRIPT/MethodName/MyParam-->​

The 4DSCRIPT tag allows you to execute 4D methods when processing the template. The presence of the <!--#4DSCRIPT/MyMethod/MyParam--> tag as an HTML comment launches the execution of the MyMethod method with the Param parameter as a string in $1.

If the tag is called in the context of a Web process, when the page is loaded, 4D calls the On Web Authentication database method (if it exists). If it returns True, 4D executes the method.

The method must return text in $0. If the string starts with the code character 1, it is considered as HTML (the same principle is true for the 4DHTML tag).

For example, let’s say that you insert the following comment “Today is <!--#4DSCRIPT/MYMETH/MYPARAM-->” into a template Web page. When loading the page, 4D calls the On Web Authentication database method, then calls the MYMETH method and passes the string “/MYPARAM” as the parameter $1. The method returns text in $0 (for example "12/31/21"); the expression "Today is <!--#4DSCRIPT/MYMETH/MYPARAM––>" therefore becomes "Today is 12/31/21".

The MYMETH method is as follows:

  //MYMETH
 C_TEXT($0;$1) //These parameters must always be declared
 $0:=String(Current date)

A method called by 4DSCRIPT must not call interface elements (DIALOG, ALERT, etc.).

As 4D executes methods in their order of appearance, it is absolutely possible to call a method that sets the value of many variables that are referenced further in the document, whichever mode you are using. You can insert as many <!--#4DSCRIPT...--> comments as you want in a template.

4DTEXT​

Syntax: <!--#4DTEXT expression-->​

Alternative syntax: $4DTEXT(expression)​

The tag <!--#4DTEXT expression--> allows you to insert a reference to a 4D variable or expression returning a value. Par exemple, si vous écrivez (dans une page HTML) :

<P>Welcome to <!--#4DTEXT vtSiteName-->!</P>

The value of the 4D variable vtSiteName will be inserted in the HTML page when it is sent. This value is inserted as simple text, special HTML characters such as ">" are automatically escaped.

Vous pouvez également insérer des expressions 4D. You can for example directly insert the contents of a field (<!--#4DTEXT [tableName]fieldName-->), an array element (<!--#4DTEXT tabarr{1}-->) or a method returning a value (<!--#4DTEXT mymethod-->). La conversion des expressions suit les mêmes règles que celles des variables. De plus, l'expression doit respecter les règles de syntaxe 4D.

For security reasons, it is recommended to use this tag when processing data introduced from outside the application, in order to prevent the insertion of malicious code.

In case of an evaluation error, the inserted text will appear as <!--#4DTEXT myvar--> : ## error # error code.

  • Vous devez utiliser des variables process.
  • Vous pouvez afficher le contenu d'un champ image. Cependant, il n'est pas possible d'afficher le contenu d'un élément de tableau d'images.
  • Il est possible d'afficher le contenu d'un champ objet à l'aide d'une formule 4D. For example, you can write <!--#4DTEXT OB Get:C1224([Rect]Desc;\"color\")-->.
  • Vous travaillerez généralement avec des variables de type Texte. Cependant, vous pouvez également utiliser des variables BLOB. You just need to generate BLOBs in Text without length mode.

Syntaxe alternative pour 4DTEXT, 4DHTML, 4DEVAL​

Plusieurs balises de transformation 4D existantes peuvent être exprimées à l'aide d'une syntaxe fondée sur le symbole $ :

4dtag (expression)​

peut être utilisé à la place de

<!--#4dtag expression-->​

Cette syntaxe alternative n'est disponible que pour les balises utilisées pour retourner des valeurs traitées :

(Les autres balises, telles que 4DIF ou 4DSCRIPT, doivent être écrites avec la syntaxe régulière).

Par exemple, vous pouvez écrire :

$4DEVAL(UserName)

au lieu de :

<!--#4DEVAL(UserName)-->

Le principal avantage de cette syntaxe est qu'elle vous permet d'écrire des modèles conformes à XML. Certains développeurs 4D ont besoin de créer et de valider des modèles basés sur XML à l'aide d'outils d'analyse syntaxique XML standard. Since the "<" character is invalid in an XML attribute value, it was not possible to use the "<!-- -->" syntax of 4D tags without breaking the document syntax. On the other hand, escaping the "<" character will prevent 4D from interpreting the tags correctly.

For example, the following code would cause an XML parsing error because of the first "<" character in the attribute value:

<line x1="<!--#4DEVAL $x-->" y1="<!--#4DEVAL $graphY1-->"/>

En utilisant la syntaxe $, le code suivant est validé par le parseur :

<line x1="$4DEVAL($x)" y1="$4DEVAL($graphY1)"/>

Note that $4dtag and <--#4dtag --> are not strictly equivalent: unlike <--#4dtag -->, $4dtag processing does not interpret 4D tags recursively. $ tags are always evaluated once and the result is considered as plain text.

Cette différence consiste à empêcher l'injection de code malveillant. As explained below, it is strongly recommended to use 4DTEXT tags instead of 4DHTML tags when handling user text to protect against unwanted reinterpretation of tags: with 4DTEXT, special characters such as "<" are escaped, thus any 4D tags using the <!--#4dtag expression --> syntax will lose their particular meaning. However, since 4DTEXT does not escape the $ symbol, we decided to break support for recursion in order to prevent malicious injection using the $4dtag (expression) syntax.

Les exemples suivants illustrent le résultat du traitement en fonction de la syntaxe et du tag utilisés :

  // example 1
 myName:="<!--#4DHTML QUIT 4D-->" //malicious injection
 input:="My name is: <!--#4DHTML myName-->"
 PROCESS 4D TAGS(input;output)
  //4D will quit!
  // example 2
 myName:="<!--#4DHTML QUIT 4D-->" //malicious injection
 input:="My name is: <!--#4DTEXT myName-->"
 PROCESS 4D TAGS(input;output)
  //output is "My name is: <!--#4DHTML QUIT 4D-->"
  // example 3
 myName:="$4DEVAL(QUIT 4D)" //malicious injection
 input:="My name is: <!--#4DTEXT myName-->"
 PROCESS 4D TAGS(input;output)
  //output is "My name is: $4DEVAL(QUIT 4D)"

Note that the $4dtag syntax supports matching pairs of enclosed quotes or parenthesis. Par exemple, supposons que vous ayez besoin d'évaluer la chaîne complexe (fictive) suivante :

String(1) + "\"(hello)\""

Vous pouvez écrire :

 input:="$4DEVAL( String(1)+\"\\\"(hello)\\\"\")"
 PROCESS 4D TAGS(input;output)
 -->output is 1"(hello)"