Extending the language / C-Extensions |
The runtime system can load several C-Extensions libraries, allowing you to properly split your libraries by defining each group of functions in separate C interface files.
Directories are searched for the C-Extensions libraries according to the FGLLDPATH environment variable rules. See environment variable definition for more details.
If the C-Extension library depends from other shared libraries, make sure that the library loader of the operating system can find theses shared objects: You may need to set the LD_LIBRARY_PATH environment variable on UNIX™ or the PATH environment variable on Windows™ to point to the directory where these other libraries are located.
There are three ways to bind a C Extension with the runtime system:
The IMPORT instruction allows you to declare an external module in a .4gl source file. It must appear at the beginning of the source file.
The name of the module specified after the IMPORT keyword is converted to lowercase by the compiler. Therefore it is recommended to use lowercase file names only.
IMPORT mylib1 MAIN CALL myfunc1("Hello World") -- C function defined in mylib1 END MAIN
When the IMPORT instruction is used, no other action has to be taken at runtime: The module name is stored in the 42m p-code and is automatically loaded when needed.
Normally, all modules using a function from a C-Extension should now use the IMPORT instruction. This could be a major change in your sources.
To simplify migration of existing C-Extensions, the runtime system loads by default a module with the name userextension. Create this shared library with your existing C-Extensions, and the runtime system will load it automatically if it is in the directories specified by FGLLDPATH.
In some cases you need several C-Extension libraries, which are used by different group of programs, so you can't use the default userextension solution. However, you don't want to review all your sources in order to use the IMPORT instruction.
fglrun -e myext1,myext2,myext3 -e myext4,myext5 myprog.42r
By using the -e option, the runtime system loads the modules specified in the command line instead of loading the default userextension module.