Restrictions for developing a user mapping plug-in (C programming language)

When you develop user mapping plugs-in in C, keep these restrictions in mind.

C-linkage

The plug-in library must be linked with C-linkage. Header files that provide the prototypes, data structures needed to implement the plug-in, and error code definitions are provided for C/C++ only. Functions that will be resolved at load time must be declared with extern "C" if the plug-in library is compiled as C++.

.NET common language runtime is not supported

The .NET common language runtime (CLR) is not supported for compiling and linking the source code for the plug-in library.

Signal handlers

The plug-in library must not install signal handlers or change the signal mask because doing so interferes with the reporting and recovering from errors. The plug-in library must never raise C++ exceptions.

Thread-safe

The plug-in library must be thread-safe and re-entrant. Only the plug-in initialization is not required to be re-entrant. The plug-in initialization function can potentially be called multiple times from different threads, in which case, the plug-in cleans up all used resources and reinitializes itself.

Overriding standard C library and operating system calls

The plug-in library must not override standard C library and operating system calls.

32-bit and 64-bit applications

A 32-bit federated server must use a 32-bit plug-in. A 64-bit federated server must use a 64-bit plug-in. In a hybrid instance, where the client is 32-bit and the server is 64-bit, the plug-in must be 64-bit.

Text strings

Input strings are not guaranteed to be null-terminated, and output strings are not required to be null-terminated. Instead, integer lengths are given for all input strings, and pointers to integers are given for lengths to be returned.