A passthru statement (used within the body of an implementation statement, described above) allows a class implementer to specify blocks of code (for C/C++ programmers, usually only #include directives) that the SOM compiler will pass into the header files it generates.
Passthru statements are included in SOM IDL primarily for backward compatibility with the SOM OIDL language, and their use by C and C++ programmers should be limited to #include directives. C and C++ programmers should use IDL type and constant declarations rather than passthru statements when possible. (Users of other languages, however, may require passthru statements for type and constant declarations.)
The contents of the passthru lines are ignored by the SOM compiler and can contain anything that needs to placed near the beginning of a header file for a class. Even comments contained in passthru lines are processed without modification. The syntax for specifying passthru lines is one of the following forms:
passthru language_suffix
where "language" specifies the programming language and "suffix" indicates which header files will be affected. The SOM Compiler supports suffixes h, ih, xh, and xih. For both C and C++, "language" is specified as C.
Each "literal" is a string literal (enclosed in double quotes) to be placed verbatim into the specified header file. [Double quotes within the passthru literal should be preceded by a backslash. No other characters escaped with a backslash will be interpreted, and formatting characters (newlines, tab characters, etc.) are passed through without processing.] The last literal for a passthru statement must not end in a backslash (put a space or other character between a final backslash and the closing double quote).
When either of the first two forms is used, passthru lines are placed before the #include statements in the header file. When the third form is used, passthru lines are placed just after the #include statements in the header file.
For example, the following passthru statement
implementation {
passthru C_h = "#include <foo.h>";
};
results in the directive #include <foo.h> being placed at the beginning of the .h C binding file that the SOM Compiler generates.
For any given target file (as indicated by language_suffix), only one passthru statement may be defined within each implementation section. You may, however, define multiple #include statements in a single passthru. For legibility, each #include should begin on a new line, optionally with a blank line to precede and follow the #include list. For an example, see "Introducing non-IDL data types or classes" later in this section.