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Re: a little c programming that no works!!

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"Heinrich Wolf" <invalid@invalid.invalid> writes:
> "Heinrich Wolf" <invalid@invalid.invalid> schrieb im Newsbeitrag 
> news:iuau65$5fc$1@news-1.m-online.net...
>>
>> ...
>> newbase resides on the stack in the scope of create_database. After you 
>> leave create_database, the memory space allocated for newbase is lost! You 
>> return the pointer newbase to the caller of create_database, but after you 
>> have left create_database, it points to freed memory. If the caller uses 
>> this pointer, this leads to a segmentation fault!
>>
>> static FILE *newbase;
>> will solve that problem.
>
> I'm sorry!
>
> I mixed it up with someting like this:
>
> char *SomeFunction(void)
>   {
>     char Buffer[10];
>     strcpy(Buffer, "Hello");
>     return Buffer;
>   }
>
> Here you need
> static char Buffer[10]; 

Or one of several other possibilities, such as having the caller pass
in a pointer to an array that will hold the result, or allocating
the result with malloc() and making the caller responsible for
free()ing it.

C's special-case semantics here lay a trap for the unwary.  The
statement "return Buffer;" *looks* like it's innocuously returning
the value of a local object, but the implicit array-to-pointer
conversion means it's really returning the address of a local objec.

-- 
Keith Thompson (The_Other_Keith) kst-u@mib.org  <http://www.ghoti.net/~kst>
Nokia
"We must do something.  This is something.  Therefore, we must do this."
    -- Antony Jay and Jonathan Lynn, "Yes Minister"

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a little c programming that no works!! Vinicio Flores <vfloreshdz@gmail.com> - 2011-06-26 20:50 -0700
  Re: a little c programming that no works!! Ian Collins <ian-news@hotmail.com> - 2011-06-27 16:07 +1200
    Re: a little c programming that no works!! Dirk Zabel <zabel@riccius-sohn.eu> - 2011-06-27 11:37 +0200
      Re: a little c programming that no works!! Ian Collins <ian-news@hotmail.com> - 2011-06-27 22:44 +1200
  Re: a little c programming that no works!! "BartC" <bc@freeuk.com> - 2011-06-27 09:44 +0100
  Re: a little c programming that no works!! Barry Schwarz <schwarzb@dqel.com> - 2011-06-27 06:04 -0700
  Re: a little c programming that no works!! "Heinrich Wolf" <invalid@invalid.invalid> - 2011-06-27 23:54 +0200
    Re: a little c programming that no works!! Lew Pitcher <lpitcher@teksavvy.com> - 2011-06-27 18:11 -0400
    Re: a little c programming that no works!! Barry Schwarz <schwarzb@dqel.com> - 2011-06-27 15:44 -0700
    Re: a little c programming that no works!! Keith Thompson <kst-u@mib.org> - 2011-06-28 22:40 -0700
    Re: a little c programming that no works!! "Heinrich Wolf" <invalid@invalid.invalid> - 2011-06-29 15:44 +0200
      Re: a little c programming that no works!! Keith Thompson <kst-u@mib.org> - 2011-06-29 10:06 -0700

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