An IDL template file contains the rules that the Software AG IDL Compiler uses - together with the IDL file - to generate interface objects, skeletons and wrappers for a programming language. The Developer's Kit provides several templates for various programming languages.
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Warning: The information in this section is intended for users who wish to write their own template files. Do not change the delivered template files. |
This document provides an introduction on how to write template files. The syntax for IDL Template Files in a formal notation is presented in the document Grammar for IDL Template Files.
This document covers the following topics:
It is the combination of control and output statements (see
control_statement, output_statement and
Using Output Statements in the Template File)
that provides the full definition of the target programming-language source
code.
Usually a template file has definition-statement grouped
together at the beginning; these are followed by loop_statements:
; type definitions
%using A "char %name%index"
....
; loop libraries
%library
{
....
; loop programs
%program
{
....
; loop parameters
%name
{
....
}
}
}
Output statements (see output_statement) provide the actual
templates of the target-language source code. Output statements are text
strings enclosed in double quotes.
These text strings may contain
output_substitution_sequence, output_formatting_sequence,
output_escape_sequence and output_of_variable.
Substitution sequences are identified by a preceding % and are substituted by their actual contents during generation.
Example: "This is a text string. The library name is %library.
\n"
The IDL Compiler provides substitution sequences for the
current library name, program name, parameter name, type, etc. Some
substitution sequences can only be accessed in their corresponding loop
statement. For example a %program substitution sequence is only valid within an
active program loop (see loop_over_programs).
See output_substitution_sequence
for a list of valid substitution sequences and description.
Formatting sequences are identified by a preceding \
Example: "\n is a Formatting sequence"
See output_formatting_sequence for
a list of valid formatting sequences
Escape sequences are identified by a preceding \\
The escape character is used to change the meaning of special
characters (&, ? and # etc.) back to their normal meaning. Special
characters are used to access variables (see
output_of_variable).
Example:"\\&".
See also output_escape_sequence and Using Verbatim Mode.
The output of variables is forced when the special characters &, ?
or # occur before the variable name (see variable_name)
in output statements (see Using Output Statements in the Template File)
Example: "?A is the output of a variable"
See also output_of_variable
The substitution sequence %type is usually used in a parameter loop
(loop_over_parameters) to generate programming-language-specific type
definitions. Before the parameter loop all IDL data types (with
definition-of-base-type-template
statements) and the dimension information (with
definition-of-index-template
statements) must be specified.
IDL data type I2 can be specified as follows in a C program:
%using %index "" "[%1_index]" "[%1_index][%2_index]" "[%1_index][%2_index][%3_index]" %using I2 "short %name%index;"
%using %index is the control_statement for the dimension information
(definition-of-index-template).
How the following strings are used depends on the dimension of the parameter.
The first empty string is used for scalar parameters, the second for
1-dimensional parameters, the third for 2-dimensional parameters and the fourth
for 3-dimensional parameters.
%using I2 is the control_statement for the IDL data type I2 (see
definition-of-base-type-template),
"short %name%index" is the output_statement for this data type.
%name and %index are substitution sequences. %name will be replaced by the
variable name and %index will be replaced by any dimension information.
If an input IDL file contained the following parameter definitions:
1 Field-1 (I2) 1 Field-2 (I2/1:8) 1 Field-3 (I2/1:4,4:7)
then, based on the above template specifications, all references to
the %type substitution sequences in any output_statement would be replaced
by
short Field_1; short Field_2[8]; short Field_3[4][4];
Special characters within some substitution sequences e.g. %library,
%program and %name can be changed during generation to provide valid names for
the target programming language. The IDL Compiler supports generation
of names for the programming languages C, C# and COBOL (see
output_control_lower_upper and
output_control_sanitize).
| Target Programming Language | Class Names | Function Names | Variable or Parameter Names |
|---|---|---|---|
| C | not applicable | %UpperCase- %LowerCase+ %Sanitize+ |
%UpperCase- %LowerCase+ %Sanitize+ |
| C# | %UpperCase- %LowerCase- %SanitizePascalCased+ |
%UpperCase- %LowerCase- %SanitizeCamelCased+ |
|
| COBOL | not applicable | %SanitizeCobol+ %UpperCase+ %LowerCase- |
The default programming language when you do not code any
output_control_lower_upper and output_control_sanitize statements in your
template is C.
Comments
are identified by a ";" in a line and
are terminated by the end of line.
For example:
; This is a comment
; So is this.
"output text followed by a comment" ; here is the comment
Whereas this is an output statement:
"an output text with a semicolon ;"
If your output is going to contain many special characters, you may
enter verbatim mode. Then all characters are written to the output as typed.
The only sequences recognized in this mode are the escape sequences (see
output_escape_sequence).
To enter verbatim mode
Use the command %verbose+ (see output_control_verbose).
Example: In verbatim mode, you enter "&" to insert an ampersand.
The IDL Compiler supports options within templates.
You can pass them with the parameter -D to the
IDL Compiler (see Starting the IDL Compiler).
Options
can be used in output statements (see
output_of_variable)
can be used in logical condition criteria (see
compare_strings) in %if (see
if_statement) and %while (see
loop_of_while) statements
are case-sensitive, i.e. hugo and HUGO are distinct options
The name of the output file is controlled by the %file statement.
If the %Format substitution sequence in a file (%file) statement is
used, the base name can be provided with the IDL Compiler parameter
-F (see Starting the IDL Compiler).
If no base name is provided with the -F IDL Compiler
parameter, the base name of the IDL file without path and extension is used as
the default of the substitution sequence %Format.
See the following excerpt from a template file:
%file "C%F.c"
When the IDL Compiler is called with
erxidl -t client.tpl .. \MyDirectory\example.idl
an output file with the default base name Cexample.c of the IDL file is created
erxidl -t client.tpl -Ftest example.idl
an output file with the name Ctest.c is created
See also the IDL Compiler option -o (see
Starting the IDL Compiler) on how to specify the directory
for the output file.
The output can be redirected to standard out with an environment
variable (see Using Options), e.g. NOOPEN. This is optional.
See the following excerpt from a template file:
%if "$(NOOPEN)" <> "1" %file "C%library.c" ;
When the IDL Compiler is called with
erxidl -t client.tpl -D NOOPEN=1 example.idl
the output is redirected to standard out
erxidl -t client.tpl example.idl
the output is directed to the file Cexample.c as specified in the template.
The IDL Compiler supports #ifdef, #elif, #else and #endif
preprocessing statements similar to the C compiler preprocessor.
You can use preprocessor variables with the option -D (see Starting the IDL Compiler).
Additional rules for #if preprocessing statements are:
If #elif is used, it must follow #ifdef.
If #else is used it must follow either #ifdef of #elif.
#endif must always close the #ifdef statement.
Embedded preprocessor statements or logical concatenation of definitions are not allowed.
See the following excerpt from a template file:
#ifdef Definition_1
"/* codes of -PDefinition_1 */\n"
%name
{
:
}
#elif Definition_2
"/* codes of -PDefinition_2 */\n"
%name
{
:
}
#else
"/* codes of neither Definition_1 nor Definition_2 */\n"
%name
{
:
}
#endif
When the IDL Compiler is called with
erxidl -t template_file -PDefinition_1
the template statements "/* codes of -PDefinition_1 */\n" between the
#ifdef and first #elif statement are interpreted.
erxidl -t template_file -PDefinition_2
the template statements "/* codes of -PDefinition_2 */\n" between the
first #elif and second #elif statement are interpreted.
erxidl -t template_file
the template statements "/* codes of neither Definition_1 nor
Definition_2 */\n" between the #else and #endif statement are interpreted.
See the following preprocessing statements with invalid syntax:
.. #ifdef (MY_VERSION) ; brackets are not allowed #endif #ifdef MY_VERSION || HIS_VERSION ; logical OR is not allowed .. #endif #ifdef (MY_VERSION) .. #ifdef (MY_NEW_VERSION) ; embedded #ifdef is not allowed
The IDL Compiler supports #include preprocessing statements
similar to the C compiler preprocessor. All statements in the included template
file are simply embedded.
To find included template files, use the IDL Compiler option
-I and add a list of directories that form a search path (see
Starting the IDL Compiler).
First the IDL Compiler searches for templates in the directory of the initial template.
When no template is found in the directory of the initial template,
all directories specified with -I are searched in the order of occurrence
Additional rules for #include preprocessing statements are:
A maximum of 32 templates can be included in a generation process.
An included template file can include further template files.
Recursive inclusion of template files is not permitted.
All variables can be accessed in all included template files as well as in the starting (root) template.
The compiler searches for included templates.
See the following excerpt from a template file:
#include "template.tpl"
The IDL Compiler supports the #trace statement to enable and disable template
tracing within a certain block of the template. The usage of
traceleveltracelevel is the same as the command-line option
"-T".
See also compiler option "-T" under
Starting the IDL Compiler for trace level values.
#trace 2 ; enable tracing on trace level 2
%compute i "0"
%while "&i" < "10"
{
%compute i "&i + 1"
}
#trace 0 ; disable