help/info/const.html

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  13 <title>const</title>
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  31 <hr>
  32 <h1>const</h1>
  33 <blockquote>
  34 <p>1. <a href="#1."> Declaring a constant of built-in type</a></p>
  35 <p>2. <a href="#2."> Declaring a constant of referenced type</a></p>
  36 <p>3. <a href="#3."> Multiple declaration of constants of the same type</a></p>
  37 <p>4. <a href="#4.">Declaring a constant array</a></p>
  38 <p>5. <a href="#5."> Declaring an external constant</a></p>
  39 </blockquote>
  40 <hr align="left" width="75%">
  41 <h4><a name="1.">1. Declaring a constant of built-in type</a></h4>
  42 <hr align="left" width="50%">
  43 <div align="center">
  44 <center>
  45 <table border="0" width="90%" bgcolor="#FFB599" cellpadding="4">
  46   <tr>
  47     <td width="100%">
  48     <h3 align="center"><font face="Courier New" color="#003258" size="5"><b>const </b></font> ( <font face="Courier New" color="#003258" size="5"><b>bitstring</b></font> | <font
  49       face="Courier New" color="#003258" size="5"><b>boolean</b></font> | <font face="Courier New" color="#003258" size="5"><b>charstring</b></font> | <font face="Courier New" color="#003258" size="5"><b>universal
  50     charstring</b></font> | <font face="Courier New" color="#003258" size="5"> <b>integer</b></font> | <font face="Courier New" color="#003258" size="5"> <b>octetstring</b></font> | <font face="Courier New"
  51       color="#003258" size="5"><b>objid</b></font> | <font face="Courier New" color="#003258" size="5"><b>hexstring</b></font> | <font face="Courier New" color="#003258" size="5"><b>verdicttype</b></font>
  52     | <font face="Courier New" color="#003258" size="5"><b>float</b></font> | <font face="Courier New" color="#003258" size="5"><b>address</b></font> | <font face="Courier New" color="#003258"
  53       size="5"><b>default</b></font> | <font face="Courier New" color="#003258" size="5"><b>anytype</b></font> ) <i>const_identifier&nbsp;</i> <font face="Courier New" color="#003258" size="5">
  54     <b>:=</b></font> <i> single_constant_expression</i> <font face="Courier New" color="#003258" size="5"> <b>;</b></font></h3>
  55     </td>
  56   </tr>
  57 </table>
  58 </center>
  59 </div>
  60 <ul>
  61   <li>
  62   <p>The <font face="Courier New" color="#003258" size="4"><b>const</b></font> keyword introduces the constant definition.</p>
  63   </li>
  64   <li>
  65   <p><a href="bitstring.html" name="par1"><font face="Courier New" color="#003258" size="4"><b>bitstring</b></font></a> denotes an a type whose distinguished values are the ordered sequences of
  66   zero, one, or more bits.</p>
  67   </li>
  68   <li>
  69   <p><a href="boolean.html"><font face="Courier New" color="#003258" size="4"><b>boolean</b></font></a> is a simple basic type consisting of two distinguished values (namely true or false).</p>
  70   </li>
  71   <li>
  72   <p><a href="charstring.html"><font face="Courier New" color="#003258" size="4"><b>charstring</b></font></a> denotes a type whose distinguished values are the ordered sequences of characters of
  73   ISO/IEC 646 as described in ITU-T Recommendation T.50.</p>
  74   </li>
  75   <li>
  76   <p><a href="universal.html"><font face="Courier New" color="#003258" size="4"><b>universal charstring</b></font></a> denotes a type whose distinguished values are the ordered sequences of UCS-4
  77   coded representation of ISO/IEC 10646 characters.</p>
  78   </li>
  79   <li>
  80   <p><a href="integer.html"><font face="Courier New" color="#003258" size="4"><b>integer</b></font></a> denotes a a type with distinguished values which are the positive and negative whole
  81   numbers, including zero.</p>
  82   </li>
  83   <li>
  84   <p><a href="octetstring.html"><font face="Courier New" color="#003258" size="4"><b>octetstring</b></font></a> stands for a a type whose distinguished values are the ordered sequences of zero or
  85   a positive even number of hexadecimal digits (every pair of digits corresponding to an ordered sequence of eight bits).</p>
  86   </li>
  87   <li>
  88   <p><a href="objid.html"><font face="Courier New" color="#003258" size="4"><b>objid</b></font></a> defines a type whose distinguished values are the set of all object identifiers conforming to
  89   clause 6.2 of ITU-T Recommendation X.660.</p>
  90   </li>
  91   <li>
  92   <p><a href="hexstring.html"><font face="Courier New" color="#003258" size="4"><b>hexstring</b></font></a> defines a type whose distinguished values are the ordered sequences of zero, one, or
  93   more hexadecimal digits, each corresponding to an ordered sequence of four bits.</p>
  94   </li>
  95   <li>
  96   <p><a href="verdicttype.html"><font face="Courier New" color="#003258" size="4"><b>verdicttype</b></font></a> defines a type for use with test verdicts consisting of 5 distinguished values.</p>
  97   </li>
  98   <li>
  99   <p><a href="float.html"><font face="Courier New" color="#003258" size="4"><b>float</b></font></a> defines a type to describe floating-point numbers.</p>
 100   </li>
 101   <li>
 102   <p><a href="address.html"><font face="Courier New" color="#003258" size="4"><b>address</b></font></a> denotes a user defined type to allow addressing specific entities inside the system under
 103   test.</p>
 104   </li>
 105   <li>
 106   <p><a href="default.html"><font face="Courier New" color="#003258" size="4"><b>default</b></font></a> is a reference to an activated default resulting from an activate operation.</p>
 107   </li>
 108 </ul>
 109 <div align="center">
 110 <center>
 111 <table border="0" width="100%" bgcolor="#C9C2BB" cellpadding="4">
 112   <tr>
 113     <td width="100%">
 114     <blockquote>&nbsp;&nbsp;&nbsp;<u>TITAN specific restriction compared to the standard</u>: anytype is not implemented yet.</blockquote>
 115     <ul>
 116       <li>
 117       <p><a href="anytype.html"><font face="Courier New" color="#003258" size="4"><b>anytype</b></font></a> defines as a shorthand for the union of all defined types, imported ASN.1 and other
 118       imported external types.</p>
 119       </li>
 120     </ul>
 121     </td>
 122   </tr>
 123 </table>
 124 </center>
 125 </div>
 126 <ul>
 127   <li>
 128   <p><i>const_identifier</i> is the&nbsp;name used to refer to the constant. Must begin with a letter, may contain letters, numbers and underscore characters.&nbsp;<br>
 129   According to the&nbsp; Naming convention, the following prefixes are recommended:&nbsp;</p>
 130   <ul>
 131     <li><b>cg_</b> for global constants (defined in the module declaration part),</li>
 132     <li><b>c_</b> for constants declared in componets and</li>
 133     <li>
 134     <p><b>cl_</b> for constants declared elsewhere.</p>
 135     </li>
 136   </ul>
 137   </li>
 138   <li>
 139   <p><i>single_constant_expression</i> may contain constants and literal values as operands. The result of the expression must correspond to the type of the constant.</p>
 140   </li>
 141 </ul>
 142 <p><a href="#Ex1">Example</a></p>
 143 <hr align="left" width="75%" color="#0094D2">
 144 <h4><a name="2.">2. Declaring a constant of referenced type</a></h4>
 145 <hr align="left" width="50%" color="#0094D2">
 146 <div align="center">
 147 <center>
 148 <table border="0" width="90%" bgcolor="#FFB599" cellpadding="4">
 149   <tr>
 150     <td width="100%">
 151     <h3 align="center"><font face="Courier New" color="#003258" size="5"><b>const </b></font> [ <i>module_id</i> [.<i>obj_id</i> ].] <i>type_reference</i> [.<i>field_reference</i> ] <i>const_identifier&nbsp;</i>
 152     <font face="Courier New" color="#003258" size="5"> <b>:=</b></font> &nbsp;<br>
 153     (<i>single_constant_expression</i> | <i>value_list</i> | <i>value_assginment_list</i>)<font face="Courier New" color="#003258" size="5"><b>;</b></font></h3>
 154     </td>
 155   </tr>
 156 </table>
 157 </center>
 158 </div>
 159 <ul>
 160   <li>
 161   <p>The <font face="Courier New" color="#003258" size="4"><b>const</b></font> keyword introduces the constant definition.</p>
 162   </li>
 163   <li>
 164   <p><i><a href="BNF.html#moduleidentifier">module_id</a></i> is needed when the referenced type is defined in another TTCN-3 module and denotes the name of that module.</p>
 165   </li>
 166 </ul>
 167 <div align="center">
 168 <center>
 169 <table border="0" width="100%" bgcolor="#C9C2BB" cellpadding="4">
 170   <tr>
 171     <td width="100%">
 172     <blockquote>&nbsp;&nbsp;&nbsp;<u>TITAN specific restriction compared to the standard</u>: objid&nbsp; is not implemented yet; it is discarded when encountered.</blockquote>
 173     <ul>
 174       <li>
 175       <p><i><a href="BNF.html#objidcomponent">obj_id</a></i> is an optional object identifier which may follow the TTCN-3 module identifier.</p>
 176       </li>
 177     </ul>
 178     </td>
 179   </tr>
 180 </table>
 181 </center>
 182 </div>
 183 <ul>
 184   <li>
 185   <p><i><a name="par2">type_reference</a></i> refers to an already defined (structured or simple) <a href="type.html">type</a>.</p>
 186   </li>
 187 </ul>
 188 <table border="0" width="100%" bgcolor="#C9C2BB" cellpadding="4">
 189   <tr>
 190     <td width="100%">
 191     <blockquote>&nbsp;&nbsp;&nbsp;<u>TITAN specific restriction compared to the standard</u>: field reference can only be used with structured constants defined in the module definition
 192     part.</blockquote>
 193     <ul>
 194       <p>
 195       <li><i><a href="BNF.html#extendedfieldreference">field_reference</a></i> optionally stands for a field of a structured type.
 196       </p>
 197       </li>
 198     </ul>
 199     </td>
 200   </tr>
 201 </table>
 202 <ul>
 203   <li>
 204   <p><i>const_identifier</i> is the&nbsp;name used to refer to the constant. Must begin with a letter, may contain letters, numbers and underscore characters.</p>
 205   </li>
 206   <li>
 207   <p><a href="BNF.html#singleconstexpression"><i>single_constant_expression</i> </a> may contain constants and literal values as operands. The result of the expression must
 208   correspond to the type of the constant. Used with simple types.</p>
 209   </li>
 210   <li>
 211   <p><a href="BNF.html#arrayconstexpression"><i>value_list</i> </a> is a comma-separated list of the constant values between curly brackets. Used with structured types.</p>
 212   </li>
 213 </ul>
 214 <div align="center">
 215 <center>
 216 <table border="0" width="100%" bgcolor="#C9C2BB" cellpadding="4">
 217   <tr>
 218     <td width="100%">
 219     <blockquote>&nbsp;&nbsp;&nbsp;<u>TITAN specific restriction compared to the standard</u>: value assignment can only be used with structured constants defined in the module definition
 220     part.</blockquote>
 221     <ul>
 222       <li>
 223       <p><a href="BNF.html#fieldconstexpressionspec"><i>value_assignment_list</i></a> is a comma-separated list of the field name - constant value pairs between curly brackets.
 224       Used with structured types.</p>
 225       </li>
 226     </ul>
 227     </td>
 228   </tr>
 229 </table>
 230 </center>
 231 </div>
 232 <p><a href="#Ex2">Example</a></p>
 233 <hr align="left" width="75%" color="#0094D2">
 234 <h4><a name="3.">3. Multiple declaration of constants of the same type</a></h4>
 235 <hr align="left" width="50%" color="#0094D2">
 236 <div align="center">
 237 <center>
 238 <table border="0" width="90%" bgcolor="#FFB599" cellpadding="4">
 239   <tr>
 240     <td width="100%">
 241     <h3 align="center"><font face="Courier New" color="#003258" size="5"><b>const </b></font> <i>type&nbsp;</i> <i>identifier<sub>1</sub>&nbsp;</i> <font face="Courier New" color="#003258"
 242       size="5"> <b>:=</b></font> <i> constant_expression<sub>1</sub></i><font face="Courier New" color="#003258" size="5"><b>,</b></font><i> identifier<sub>2</sub>&nbsp;</i> <font face="Courier New"
 243       color="#003258" size="5"> <b>:=</b></font> <i> constant_expression<sub>2</sub> …</i> <font face="Courier New" color="#003258" size="5"> <b>;</b></font></h3>
 244     </td>
 245   </tr>
 246 </table>
 247 </center>
 248 </div>
 249 <ul>
 250   <li>
 251   <p>The <font face="Courier New" color="#003258" size="4"><b>const</b></font> keyword introduces the constant definition.</p>
 252   </li>
 253   <li>
 254   <p align="left"><i>type</i> is one of the built-in types mentioned in <a href="#par1">paragraph 1</a> or referenced types mentioned in <a href="#par2">paragraph 2</a> .</p>
 255   </li>
 256   <li>
 257   <p><i>identifier<sub>n</sub></i> is the&nbsp;name used to refer to the n<sup>th</sup> constant.</p>
 258   </li>
 259   <li>
 260   <p><i>constant_expression<sub>n</sub></i> determines the value of the n<sup>th</sup> constant.</p>
 261   </li>
 262 </ul>
 263 <p><a href="#Ex3">Example</a></p>
 264 <hr align="left" width="75%" color="#0094D2">
 265 <h4><a name="4.">4. Declaring a constant array</a></h4>
 266 <hr align="left" width="50%" color="#0094D2">
 267 <div align="center">
 268 <center>
 269 <table border="0" width="90%" bgcolor="#FFB599" cellpadding="4">
 270   <tr>
 271     <td width="100%">
 272     <h3 align="center"><font face="Courier New" color="#003258" size="5"><b>const </b></font> <i>type const_identifier </i> <font face="Courier New" color="#003258" size="5"><b>[ </b></font> <i>array_index</i>
 273     <font face="Courier New" color="#003258" size="5"><b> ] :=</b></font> <i>value_list</i><font face="Courier New" color="#003258" size="5"><b>;</b></font></h3>
 274     </td>
 275   </tr>
 276 </table>
 277 </center>
 278 </div>
 279 <ul>
 280   <li>
 281   <p>The <font face="Courier New" color="#003258" size="4"><b>const</b></font> keyword introduces the constant definition.</p>
 282   </li>
 283   <li>
 284   <p align="left"><i>type</i> is one of the built-in types mentioned in <a href="#par1">paragraph 1</a> or referenced types mentioned in <a href="#par2">paragraph 2</a> .</p>
 285   </li>
 286   <li>
 287   <p><i>const_identifier</i> is the&nbsp;name used to refer to the constant. Must begin with a letter, may contain letters, numbers and underscore characters.</p>
 288   </li>
 289   <li>
 290   <p><i><a href="BNF.html#arraydef">array index</a></i> is a non-negative integer value corresponding to the number of elements in the array.&nbsp;<br>
 291   &nbsp;&nbsp;&nbsp; Alternatively, the lower and upper index values are given joined by two dots.</p>
 292   </li>
 293   <li>
 294   <p><a href="BNF.html#arrayconstexpression"><i>value_list</i> </a> is a comma-separated list of the constant values between curly brackets.</p>
 295   </li>
 296 </ul>
 297 <p><a href="#Ex4">Example</a></p>
 298 <hr align="left" width="75%" color="#0094D2">
 299 <h4><a name="5.">5. Declaring an external constant</a></h4>
 300 <hr align="left" width="50%" color="#0094D2">
 301 <div align="center">
 302 <center>
 303 <table border="0" width="90%" bgcolor="#FFB599" cellpadding="4">
 304   <tr>
 305     <td width="100%">
 306     <h3 align="center"><font face="Courier New" color="#003258" size="5"><b>external const </b></font> <i>type const_identifier </i> <font face="Courier New" color="#003258" size="5"><b>;</b></font>
 307     </h3>
 308     </td>
 309   </tr>
 310 </table>
 311 </center>
 312 </div>
 313 <ul>
 314   <li>
 315   <p>The <font face="Courier New" color="#003258" size="4"><b>external</b></font> keyword means that the constant is defined in a module other than TTCN-3 or ASN.1 (for example in a module written
 316   in C++).</p>
 317   </li>
 318   <li>
 319   <p>The <font face="Courier New" color="#003258" size="4"><b>const</b></font> keyword introduces the constant definition.</p>
 320   </li>
 321   <li>
 322   <p align="left"><i>type</i> is one of the built-in types mentioned in <a href="#par1">paragraph 1</a> or referenced types mentioned in <a href="#par2">paragraph 2</a> .</p>
 323   </li>
 324   <li>
 325   <p><i>const_identifier</i> is the&nbsp;name used to refer to the constant. Must begin with a letter, may contain letters, numbers and underscore characters.</p>
 326   </li>
 327 </ul>
 328 <p><a href="#Ex5">Example</a></p>
 329 <hr align="left" width="50%">
 330 <hr align="left" width="50%">
 331 <p><a name="Ex1">Example 1a</a>:
 332 <p><font face="Courier New">const integer c_myConstant := 127;</font>
 333 <p>A constant called c_MyConstant is defined. The constant will have the value one hundred twenty seven.</p>
 334 <p>&nbsp;</p>
 335 <p>Example 1b:
 336 <p><font face="Courier New">const bitstring c_myGarland := '00101101'B;&nbsp;<br>
 337 const bitstring c_myBiggerGarland := c_myGarland &amp; '11000010'B;</font></p>
 338 <p>Two constants are defined. The one called c_myBiggerGarland will have the binary value 11101111.</p>
 339 <p>&nbsp;</p>
 340 <p><a name="Ex2">Example 2a</a>:
 341 <p><font face="Courier New">type record E_Rec {integer field1, boolean field2}; //defined in Elsewhere</font></p>
 342 <p><font face="Courier New">const Elsewhere.E_Rec c_CurrConst := {17, true};</font></p>
 343 <p>A record called E_Rec have been defined in the TTCN-3 module Elsewhere. In the current module we define a constant named c_CurrConst and assign values to all of its fields. In TITAN, the value
 344 notation as shown above may only be used in the module definition part.</p>
 345 <p>&nbsp;</p>
 346 <p>Example 2b:
 347 <p><font face="Courier New">type record G_Rec {float first_field, hexstring last_field};&nbsp;<br>
 348 const G_Rec.last_field c_FuzerConst := 'AA'H;</font></p>
 349 <p>First we define a record called G_Rec. Then we define a constant named c_FuzerConst derived from the second field of the referred type and assign the hexadecimal value AA to it.&nbsp;</p>
 350 <p>&nbsp;</p>
 351 <p>Example 2c:
 352 <p><font face="Courier New">type record G_Rec {float first_field, hexstring last_field};&nbsp;<br>
 353 const G_Rec c_UeppigConst := {<br>
 354 &nbsp;&nbsp;&nbsp; first_field := 5.77,<br>
 355 &nbsp;&nbsp;&nbsp; last_field := '55'H;<br>
 356 }</font></p>
 357 <p>First we define a record called G_Rec. Then we define a constant named c_UeppigConst and assign values to both of its fields using assignment notation.</p>
 358 <p>&nbsp;</p>
 359 <p><a name="Ex3">Example 3</a>:
 360 <p><font face="Courier New">const boolean c_MyConst2 := true, c_MyConst3 := false;</font></p>
 361 <p>Two constants (c_MyConst2 and c_MyConst3) are declared within one operation.&nbsp;</p>
 362 <p>&nbsp;</p>
 363 <p><a name="Ex4">Example 4a</a>:
 364 <p><font face="Courier New">const boolean c_MinConst[3] := { true, false, false };</font></p>
 365 <p>The array defined c_MinConst consists of three elements indexed from 0 to 2.</p>
 366 <p>&nbsp;</p>
 367 <p>Example 4b:
 368 <p><font face="Courier New">const boolean c_DinConst[7..9] := { true, false, false };</font></p>
 369 <p>The array defined c_DinConst consists also of three elements as in the example 4a, but here the indices run from 7 to 9.</p>
 370 <p>&nbsp;</p>
 371 <p><a name="Ex5">Example 5</a>:
 372 <p><font face="Courier New">external const objid MonConst;</font></p>
 373 <p>The constant called MonConst (an object identifier) is defined in an external module, e.g. in a module written in C++.</p>
 374 <hr align="left" width="25%">
 375 <hr align="left" width="25%">
 376 <p><a HREF="BNF.html#constdef">BNF definition</a> of <font face="Courier New"> const</font></p>
 377 </body>
 378 </html>