Check the API version of a library

When you invoke the Informix® ESQL/C application that is linked with shared HCL Informix® general libraries, the release number of these shared libraries must be compatible with that of the shared libraries in the $INFORMIXDIR/lib or the %INFORMIXDIR%\lib directory.

In a Windows™ environment, a developer can easily verify the name of the shared library DLL, namely isqltnnx.dll, where nn stand for the version number, and x stand for the API version.

For the Informix® ESQL/C application on UNIX™, however, given that the linked libraries get symbolic names, it is not easy to find the version number of the linked library. Therefore, Informix® ESQL/C does this check for you. Informix® ESQL/C performs an internal check between the API version of the library that the application uses and the API version of the library that is installed as part of your Informix® ESQL/C product. Format of the Informix shared-library name shows where the API version appears in the shared library name.

Informix® ESQL/C uses the HCL Informix® function that is called checkapi() to perform this check. The checkapi() function is in the checkapi.o object file, which is contained in the $INFORMIXDIR/lib/esql directory. The esql command automatically links this checkapi.o object file with every executable that it creates.

To determine the API version of the library that the application uses, Informix® ESQL/C checks the values of special macro definitions in the executable file. When the Informix® ESQL/C preprocessor processes a source file, it copies the macro definitions from the sqlhdr.h header file into the C source file (.c) that it generates. The following example shows sample values for these macros:

#define CLIENT_GEN_VER                  710
#define CLIENT_OS_VER                  710
#define CLIENT_SQLI_VER                  710
#define CLIENT_GLS_VER                  710

Tip: The Informix® ESQL/C preprocessor automatically includes the sqlhdr.h file in all Informix® ESQL/C executable files that it generates.

If the API version of the libraries in this executable file is not compatible, Informix® ESQL/C returns a runtime error that indicates which library is not compatible. You must recompile your Informix® ESQL/C application to link the new release version of the shared library.

If you do not use esql to link one of the shared Informix® general libraries with your Informix® ESQL/C application, you must explicitly link the checkapi.o file with your application. Otherwise, Informix® ESQL/C might generate an error at link time of the form:

undefined ifx_checkAPI()