in reply to Re: Win32::API Memory Exception with GetCommandLine() (which returns a static string)
in thread Win32::API Memory Exception with GetCommandLine() (which returns a static string)

At the core of Win32::API are several small piece of assembler code: 

#if (defined(__BORLANDC__) && __BORLANDC__ >= 452)
    #define ASM_LOAD_EAX(param,type)  {   \
        __asm {                      \
            mov    eax, type param ; \
            push   eax             ; \
        }
/* MSVC compilers */
#elif defined _MSC_VER
    /* Disable warning about one missing macro parameter.
       TODO: How we define a macro with an optional (empty) parameter?
+ */
    #pragma warning( disable : 4003 )
    #define ASM_LOAD_EAX(param,type) { \
    __asm { mov eax, type param }; \
    __asm { push eax };            \
    }
/* GCC-MinGW Compiler */
#elif (defined(__GNUC__))
    #define ASM_LOAD_EAX(param,...)  asm ("push %0" :: "g" (param));
#endif

...
              ASM_LOAD_EAX(pParam, dword ptr); ## many similar

...

#if (defined(_MSC_VER) || defined(BORLANDC))
                __asm {
                    mov   eax, dword ptr [dParam + 4]  ;
                    push  eax                          ;
                    mov   eax, dword ptr [dParam]      ;
                    push  eax                          ;
                };
#elif (defined(__GNUC__))
/* probably uglier than necessary, but works */
asm ("pushl %0":: "g" (((unsigned int*)&dParam)[1]));
asm ("pushl %0":: "g" (((unsigned int*)&dParam)[0]));

/* { 
  int idc;
  printf ("dParam = ");
  for (idc = 0; idc < sizeof(dParam); idc++) {
    printf(" %2.2x",((unsigned char*)&dParam)[idc]);
  } 
  printf("   %f\n", dParam);
} */
#endif

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One has to suspect, if the OP confirms he is using a mingw built version of Perl that the problem lies in there somewhere. Does mingw build using similar calling conventions to MSC? That is the PASCAL calling convention for system apis.

Examine what is said, not who speaks -- Silence betokens consent -- Love the truth but pardon error.
"Science is about questioning the status quo. Questioning authority".
In the absence of evidence, opinion is indistinguishable from prejudice.
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  • Comment on Re^2: Win32::API Memory Exception with GetCommandLine() (which returns a static string)
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Re^3: Win32::API Memory Exception with GetCommandLine() (which returns a static string)
by syphilis (Archbishop) on Jul 06, 2007 at 05:30 UTC
    One has to suspect, if the OP confirms he is using a mingw built version of Perl that the problem lies in there somewhere

    There's a couple of different possibilities:
    1)It's MinGW-built perl using MinGW-built Win32::API;
    2)It's MinGW-built perl using VC-built Win32::API;

    I'm in the second category (with Win32-API-0.46). I also have Win32-API-0.46 on ActiveState perl (build 819) - it is exactly the same binary as I'm running on my MinGW-built perl, but there's no GPF with ActivePerl ... which leads me to the conclusion that the problem might lie outside Win32::API.

    I still get the same length discrepancy on ActivePerl - ie Inline's 20 vs Win32::API's 21.

    Cheers,
    Rob
[reply]
      I still get the same length discrepancy on ActivePerl - ie Inline's 20 vs Win32::API's 21.

      I have a vague recollection that somewhere in Win32::API, they have code to extend the length of various strings/buffers passed in and/or out by one to 'allow room for terminating nulls'.

      Maybe I'm too tired or mis-remembering, because I cannot find it now? :(

      Examine what is said, not who speaks -- Silence betokens consent -- Love the truth but pardon error.
      "Science is about questioning the status quo. Questioning authority".
      In the absence of evidence, opinion is indistinguishable from prejudice.
[reply]
        I've just noticed that if I take the OP's code out of the batch file, it works ok (no faults) though it still returns the wrong string.

        Also, if I replace the OP's code in the batch file with: 
        use Win32::API;

$function = new Win32::API("kernel32", "GetCommandLine", '', 'P');

$string = $function->Call();

print "string[".length($string)."] = '$string'\n";

        [download]
        then the batch file runs without error and $string no longer contains the additional trailing space - ie Win32::API and Inline are in complete agreement.

        A problem with the Import method perhaps ? ... I've never trusted it.

        Cheers,
        Rob
        Update: As BrowserUk has subsequently demonstrated, it's the pack('Z*', ...) that leads to the extra trailing space - nothing to do with Win32::API->Import() at all.
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