odd line in windows

xiaoyafeng has asked for the wisdom of the Perl Monks concerning the following question:

Hi monks,

I wrote a simple snippet to list processes name and pid on windows. but the output returns a strange line. below is the code:

use strict;
use warnings;

use Inline C => DATA =>
           LIBS => '-luser32 -lkernel32 -lpsapi';

my $a = process_list();
map { print; print get_proc_name($_);print "\n"; } @{$a};


__END__
__C__

#include <windows.h>
#include <stdio.h>
#include <tchar.h>
#include <psapi.h>

char* get_proc_name( int processID )
{
    TCHAR szProcessName[MAX_PATH] = TEXT("<unknown>");


    HANDLE hProcess = OpenProcess( PROCESS_QUERY_INFORMATION |
                                   PROCESS_VM_READ,
                                   FALSE, processID );


    if (NULL != hProcess )
    {
        HMODULE hMod;
        DWORD cbNeeded;

        if ( EnumProcessModules( hProcess, &hMod, sizeof(hMod), 
             &cbNeeded) )
        {
            GetModuleBaseName( hProcess, hMod, szProcessName, 
                               sizeof(szProcessName)/sizeof(TCHAR) );
        }
    }

    CloseHandle( hProcess );
    return szProcessName;
}





SV* process_list(){

DWORD aProcesses[1024], cbNeeded, cProcesses;
    unsigned int i;
EnumProcesses( aProcesses, sizeof(aProcesses),  &cbNeeded );

cProcesses = cbNeeded / sizeof(DWORD);
AV* AV_procs = newAV();
    for ( i = 0; i < cProcesses; i++ )
    {
        if( aProcesses[i] != 0 )
        {
            av_push(AV_procs, newSViv( aProcesses[i] ) );
        }
    }
    return newRV_inc(AV_procs);
}



__OUTPUT__

C:\>perl test.pl
4P ?F >                       <==    strange line
292<unknown>
372<unknown>
432<unknown>
[download]

I post this question on Inline and Sisyphus (many Thanks! Sisyphus) replied me and suggest me posting this question on perlmonks for help. here is his reply:


Haven't yet had a chance to take a thorough look at this.
I inserted the following near the beginning of your script:

use Inline C => Config =>
  BUILD_NOISY => 1;

That way you get to see any compiler warnings that are emitted during 
+the C compilation, and with my cc-4.5.2 build of perl-5.14 I saw:

try_pl_f4a3.xs: In function 'get_proc_name':
try_pl_f4a3.xs:35:1: warning: function returns address of local variab
+le
try_pl_f4a3.xs: In function 'process_list':
try_pl_f4a3.xs:57:5: warning: passing argument 2 of 'Perl_newRV' from 
+incompatible pointer type
C:\MinGW\perl\lib\CORE/proto.h:2567:19: note: expected 'struct SV * co
+nst' but argument is of type 'struct AV *'

Whether there's anything relevant there, I don't know.

I get different output to you, of course. But in the middle of the out
+put I also got one odd-looking line:

1348&#9508;aæ&#9787;&#8593;:ñ $   &#8593;:ñ  ~&#8593;&#9787;

When I switched to a gcc-3.4.5 build of perl-5.12, I found out what 13
+48 really was:
1348TomTomHOMERunner.exe

But then I got a strange line at the beginning of the output:

4ð¬&#9472;w4§Å &#8593;
whereas, with gcc-4.5.2, that had been:
4<unknown>
[download]

Thanks in advance!!!

I am trying to improve my English skills, if you see a mistake please feel free to reply or /msg me a correction

Comment on odd line in windows Select or Download Code

Replies are listed 'Best First'.
Re: odd line in windows by BrowserUk (Patriarch) on Sep 07, 2011 at 07:52 UTC
The likely cause is identified by `try_pl_f4a3.xs: In function 'get_proc_name': try_pl_f4a3.xs:35:1: warning: function returns address of local variab +le` [download] Which is telling you that this: `char* get_proc_name( int processID ) { TCHAR szProcessName[MAX_PATH] = TEXT("<unknown>"); ... return szProcessName; }` [download] Is a fundamentally flawed piece of code. You are allocating a string on the stack, and then returning a pointer to it from the function. But when the function returns, the stack is unwound and can be reused by other parts of the code. The only surprising thing here is that you actually get something returned and it doesn't crash. You need to correct that by allocating space on the heap using Newx() or Newxc() or Newxz(). See perlapi That said. I wonder why you aren't using Win32::Process::Info? 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] [d/l] [select]
Re^2: odd line in windows by xiaoyafeng (Deacon) on Sep 07, 2011 at 09:22 UTC
Many Thanks, BrowserUk! Returning a variable on stack is a fundamental mistake indeed. I change `TCHAR szProcessName[MAX_PATH] = TEXT("<unknown>");` into `TCHAR * szProcessName = (TCHAR) malloc( MAX_PATH sizeof(TCHAR) );` [download] it looks like working well now. but sequenced question is, how free this memory I allocate in C? That said. I wonder why you aren't using Win32::Process::Info? I don't using Wi32::Process::Info is because it's running a bit slowly. it uses variable way to get Process info and return too large info to me. In my case, I just want to check process name. I am trying to improve my English skills, if you see a mistake please feel free to reply or /msg me a correction	[reply] [d/l] [select]
Re^3: odd line in windows by BrowserUk (Patriarch) on Sep 07, 2011 at 09:39 UTC
I change `= TEXT("<unknown>");` into `= (TCHAR) malloc( MAX_PATH * sizeof(TCHAR) );` it looks like working well now. but sequenced question is, how free this memory I allocate in C?* You should not be using `malloc()`. Did you miss my mention of `Newx(), Newxc() Newxz()` and the associated link? how free this memory I allocate in C? If you followed the link, you would have seen `Safefree()` In my case, I just want to check process name. I tend to use tasklist for that: perl -E"my @tasks = map[ (split)[0,1] ], `tasklist /nh`; say qq[@$_] f +or @tasks" [download] 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] [d/l] [select]
Re^3: odd line in windows by Anonymous Monk on Sep 07, 2011 at 09:27 UTC
Read perlclib, use Safefree	[reply]
Re^3: odd line in windows by syphilis (Archbishop) on Sep 07, 2011 at 15:14 UTC
but sequenced question is, how free this memory I allocate in C? One way is to create a copy, free the memory, then return the copy. The following rewrite of get_proc_name() works for me, and frees the memory: SV * get_proc_name( int processID ) { char * szProcessName; SV * outsv; Newxz(szProcessName, MAX_PATH, char); HANDLE hProcess = OpenProcess ( PROCESS_QUERY_INFORMATION \| PROCESS_VM_READ, FALSE, processID ); if (NULL != hProcess ) { HMODULE hMod; DWORD cbNeeded; if ( EnumProcessModules( hProcess, &hMod, sizeof(hMod), &cbNee +ded) ) { GetModuleBaseName( hProcess, hMod, szProcessName, MAX_PATH + - 1); } else { szProcessName[0] = '#'; szProcessName[1] = 0; } } else { szProcessName[0] = '*'; szProcessName[1] = 0; } CloseHandle( hProcess ); outsv = newSVpv(szProcessName, 0); Safefree(szProcessName); return outsv; } [download] Cheers, Rob	[reply] [d/l]
Re^4: odd line in windows by BrowserUk (Patriarch) on Sep 07, 2011 at 15:37 UTC
Re^5: odd line in windows by syphilis (Archbishop) on Sep 07, 2011 at 16:30 UTC
Re: odd line in windows by syphilis (Archbishop) on Sep 07, 2011 at 16:06 UTC
try_pl_f4a3.xs:57:5: warning: passing argument 2 of 'Perl_newRV' from incompatible pointer type This warning is in response to: `return newRV_inc(AV_procs);` [download] and I think that's not quite the right thing to be doing. According to perlapi, newRV_inc() takes an SV* arg, but `AV_procs` is an AV. Rewriting process_list() as follows avoids the warning, and intuitively strikes me as being a better approach: `AV process_list(){ DWORD aProcesses[1024], cbNeeded, cProcesses; unsigned int i; EnumProcesses( aProcesses, sizeof(aProcesses), &cbNeeded ); cProcesses = cbNeeded / sizeof(DWORD); AV* AV_procs = newAV(); for ( i = 0; i < cProcesses; i++ ) { if( aProcesses[i] != 0 ) { av_push(AV_procs, newSViv( aProcesses[i] ) ); } } return AV_procs; }` [download] Cheers, Rob	[reply] [d/l] [select]
Re^2: odd line in windows by xiaoyafeng (Deacon) on Sep 08, 2011 at 07:49 UTC
new function does avoid the warning, but what does AV* mean in perl? a SV* are able to be a reference of array other than a AV. though I'm still digging how this warning come, I insist using SV as returning. I am trying to improve my English skills, if you see a mistake please feel free to reply or /msg me a correction	[reply]
Re^3: odd line in windows by ikegami (Patriarch) on Sep 08, 2011 at 09:26 UTC
The typemap automatically creates a reference to it and returns the reference. It's refcount is off by one, though. `use strict; use warnings; use Devel::Peek qw( Dump ); use Inline C => <<'__EOI__'; AV* f() { return newAV(); } __EOI__ Dump(f());` [download] `>perl -MInline=FORCE,NOISY,NOCLEAN a.pl ... SV = IV(0x7bbf18) at 0x7bbf1c REFCNT = 1 FLAGS = (TEMP,ROK) RV = 0x7bc05c SV = PVAV(0x7bcec8) at 0x7bc05c REFCNT = 2 <--- XXX FLAGS = () ARRAY = 0x0 FILL = -1 MAX = -1 ARYLEN = 0x0 FLAGS = (REAL)` [download] Making it mortal doesn't help. So unless I'm missing something, this can only be used if you actually hold a reference to the array you return.	[reply] [d/l] [select]
Re^4: odd line in windows by syphilis (Archbishop) on Sep 08, 2011 at 10:58 UTC
Re^5: odd line in windows by BrowserUk (Patriarch) on Sep 08, 2011 at 11:12 UTC
Some notes below your chosen depth have not been shown here
Re^5: odd line in windows (WONTFIX) by ikegami (Patriarch) on Sep 09, 2011 at 03:20 UTC
Re^5: odd line in windows by ikegami (Patriarch) on Sep 08, 2011 at 19:53 UTC
Re^2: odd line in windows by ikegami (Patriarch) on Sep 08, 2011 at 07:13 UTC
and I think that's not quite the right thing to be doing. According to perlapi, newRV_inc() takes an SV arg, but AV_procs is an AV. An AV is a type of SV. That's indeed the way to create a reference to an array. You just need to cast. `newRV_noinc(MUTABLE_SV(av))` [download]	[reply] [d/l]

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