Extending the language

Parent topic: Extending the language

C-Extensions

With C-Extensions, you can bind your own C libraries in the runtime system, to call C function from the application code.

Understanding C-Extensions
C-Extensions allow you to write custom shared libraries in the C language.
Header files for ESQL/C typedefs
C header files (.h) are required to define C structures for complex data types used in a C-Extension.
Creating C-Extensions
Custom C-Extensions must be provided to the runtime system as Shared Objects (.so) on UNIX™, and as Dynamically Loadable Libraries (.DLL) on Windows®.
Creating Informix ESQL/C Extensions
C-Extension libraries can be created from ESQL/C sources, as long as you have an Informix® ESQL/C compiler which is compatible with your Genero runtime system.
The C interface file
To make your C functions visible to the runtime system, you must define all the functions in the C interface file.
Linking programs using C-Extensions
When creating a 42r program or 42x library, the linker needs to resolve all function names, including C-Extension functions.
Loading C-Extensions at runtime
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.
Runtime stack functions
To pass values between a C function and a program, the C function and the runtime system use the runtime stack.
Data types and structures
C types are used to write C-Extensions.
NULL handing
Handling NULL in C-Extensions.
Calling C functions from programs
C-Extensions functions can be called from the program in the same way that you call a BDL function.
Calling program functions from C
It is possible to call a BDL function from a C-Extension function.
Simple C-Extension example
This example shows how to create a C-Extension library on Linux® using gcc.
Implementing C-Extensions for GMI
This section describes how to program C-Extensions for the GMI VM.

Parent topic: Extending the language