In some compilers and compile modes this is also fairly easy to do. A lot of compilers do not offer priority, and are impossible to maintain an order in. Some compilers only provide startup priority for C++ mode. This system works as long as there is a way to run a single function at some point before main() and after C runtime initializes. 

In Windows, you might think you have this ability with DllMain, but there are severe limitations that you would have to get around; primary is the inability to create a thread, well, you can create it, but it will remain suspended until you leave DllMains and all DllMains finish. There is also no way to consistantly provide initialization order, like memory needs to be initialized before anything else.

This schedules a routine to run at startup. Fill in the routine with the code you want, and it will run at DEFAULT_PRELOAD_PRIORITY which is the number 69. 

  
PRELOAD( MyCustomInit )
{
    // do something here (do anything here,
    // without limitations that are imposed by DllMain/LibMain.
}

If you wanted a routine which was guaranteed to run before MyCustomInit you might use PRIORITY_PRELOAD whcih allows you to specify a priority.

  
PRIORITY_PRELOAD( MyOtherInit, DEFAULT_PRELOAD_PRIORITY-10 )
{
   // this will run before other things.
}

Priorities are listed in deadstart.h and exit_priorities.h. The priorities are treated backwards, so low number startup priorities go first, and higher number shutdown priorities go first. 

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