How to explicitly call CRT startup functions

Question

Is there any way I can explicitly in my code call the functions that are normally called in mainCRTStartup functions? I'm specifically interested initterm and initterm_e functions. Even thought my program is linked with crt (it has to be, right?) I couldn't just call initterm - I tried to declare and just invoke and I got undefined reference.

Is there any way to do it?

It is not exported so you can't link it. Which is for the better, doing this is unlikely to come to good end. Just restart the program. — Hans Passant, Sep 20 '17 at 21:18
@HansPassant - no, this api is exported. say by *msvcrt.dll*. and in lib files we can found this names too — RbMm, Sep 20 '17 at 21:21
*my program is linked with crt* - which *lib* exactly you use ? you need open this lib and search for `initterm` string. think it exist and lib file and undefined reference only because you wrong declared it — RbMm, Sep 20 '17 at 21:27
for example if use say *ucrt.lib* here exist both *initterm* and was bind to `api-ms-win-crt-runtime-l1-1-0.dll`. in other words to `ucrtbase.dll`. another crt libs can bind to another dlls. and this functions very easy implement yourself too — RbMm, Sep 20 '17 at 21:32
*Is there any way to do it?* of course yes and very simply - correct declare it and call. or you have problems with input parameters ? like `#pragma const_seg(".CRT$XCA") const _PVFV __xc_a = 0; #pragma const_seg(".CRT$XCZ") const _PVFV __xc_z = 0;` and call `_initterm(&__xc_a, &__xc_z);` — RbMm, Sep 20 '17 at 21:40
Oh how silly of me. In the declaration I didn't state that its c function (in programming in c++). So the name got mangled. — Marcin K., Sep 20 '17 at 21:51
From the documentation: **"Do not call these methods in a program."** — Harry Johnston, Sep 20 '17 at 21:53
The real question is; *why* do you want (or need) to do this? — Jesper Juhl, Sep 20 '17 at 22:02
My project has special requirements that require me to do ugly stuff @RbMm If you would make your comment into answer I would mark it — Marcin K., Sep 20 '17 at 22:34

score 3 · Accepted Answer · answered Sep 20 '17 at 23:33

the _initterm, and _initterm_e (note in msdn _initterm_e is wrong declared - really it used _PIFV type) is exported by different CRT dlls. and it declared in lib files too. and implementation of this functions is very simply:

typedef void (__cdecl *_PVFV)();

void _initterm(const _PVFV *ppfn, const _PVFV *end)
{
    do 
    {
        if (_PVFV pfn = *++ppfn)
        {
            pfn();
        }
    } while (ppfn < end);
}

typedef int  (__cdecl *_PIFV)();

int _initterm_e(const _PIFV *ppfn, const _PIFV *end)
{
    do 
    {
        if (_PIFV pfn = *++ppfn)
        {
            if (int err = pfn()) return err;
        }
    } while (ppfn < end);

    return 0;
}

so you can import it ot use own implementation. here faster question - what is use as input parameters ?

say c++ (CL compiler how minimum) use ( ".CRT$XCA", ".CRT$XCZ" ) sections for place c++ global initializes. so we can do next:

extern "C"
{
#pragma const_seg(".CRT$XCA")
  const _PVFV __xc_a = 0;
#pragma const_seg(".CRT$XCZ")
  const _PVFV __xc_z = 0;

#pragma const_seg(".CRT$XIA")
  const _PVFV __xi_a = 0;
#pragma const_seg(".CRT$XIZ")
  const _PVFV __xi_z = 0;
}

    /*
     * do initializations
     */
    initret = _initterm_e( &__xi_a, &__xi_z );
    if ( initret != 0 )
        return initret;

    /*
     * do C++ initializations
     */
    _initterm( &__xc_a, &__xc_z );

but here need very good understand - what and why we doing

Thanks. Just a fast clarification: Shouldnt function pointer be postincremented instead of preincremented? — Marcin K., Sep 21 '17 at 08:55
@MarcinK. - i use `__xc_a` as pointer begin. so `ppfn` at begin will be point exactly to `__xc_a` which is 0. so `*ppfn` at begin is 0. preincremented is small optimization. but if use postincrement will be no error — RbMm, Sep 21 '17 at 09:11

How to explicitly call CRT startup functions

1 Answers1