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Meaning Abbreviation Notation line feed NL (LF) \n horizontal tabulator HT \t vertical tabulator VT \v backspace BS \b carriage return CR \r form feed FF \f bell BEL \a backslash \ \\ single quote ’ \’ arbitrary character (hexadecimal) \xnn arbitrary character (octal) \0nnn Table 7.1: Surrogates for special characters. true. Please note that some HALCON operators take logical values for input (e.g., set_system). In this case the HALCON operators expect string constants like ’true’ or ’false’ rather than the boolean values true or false. In addition to these general types, there are special constants and the type tuple, which are specific to HALCON or HDevelop, respectively. constants There are constants for the return value (result state) of an operator. The constants can be used together with the operator dev_error_var and dev_set_check. These constants represent the normal return value of an operator, so called messages. For errors no constants are available (there are more than 400 error numbers internally, see the Extension Package Programmer’s Manual). In table 7.2 all return messages can be found. tuple The control types are only used within the generic HDevelop type tuple. A tuple of length 1 is interpreted as an atomic value. A tuple may consist of several numerical data items with different types. The standard representation of a tuple is a listing of its elements included into brackets. This is illustrated in figure 7.1. Constant Meaning Value H_MSG_TRUE No error; for tests: (true) 2 H_MSG_FALSE For tests: false 3 H_MSG_VOID No result could be computed 4 H_MSG_FAIL Operator did not succeed 5 Table 7.2: Return values for operators. 269 Language 7.2 Control Types and Constants
