Object code that the XL Fortran compiler produces often invokes compiler-supplied subprograms at run time to handle certain complex tasks. These subprograms are collected into several libraries.
The function of the XL Fortran Run-Time Environment may be divided into these main categories:
The XL Fortran Run-Time Environment also produces run-time diagnostic messages in the national language appropriate for your system. Unless you bind statically, you cannot run object code produced by the XL Fortran compiler without the XL Fortran Run-Time Environment.
The XL Fortran Run-Time Environment is upward-compatible. Programs that are compiled with a given level of the run-time environment and a given level of the AIX operating system require the same or higher levels of both the run-time environment and the operating system to run.
Run-time subprograms are collected into libraries. By default, the compiler invocation command also invokes the linker and gives it the names of the libraries that contain run-time subprograms called by Fortran object code.
The names of these run-time subprograms are external symbols. When object code that is produced by the XL Fortran compiler calls a run-time subprogram, the .o object code file contains an external symbol reference to the name of the subprogram. A library contains an external symbol definition for the subprogram. The linker resolves the run-time subprogram call with the subprogram definition.
You should avoid using names in your XL Fortran program that conflict with names of run-time subprograms. Conflict can arise under two conditions: