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Date: Wed, 20 Jul 2011 20:45:11 +0300
From: Eli Zaretskii <eliz AT gnu DOT org>
Subject: Re: printf statement causes error message
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> From: Mok-Kong Shen <mok-kong DOT shen AT t-online DOT de>
> Date: Wed, 20 Jul 2011 18:58:58 +0200
> Bytes: 1820
> 
> Could some expert kindly tell why the one printf statement in the
> main program below causes the trouble?

Because you try to `free' a pointer whose value is garbage?

Here:

> void test()
> { int *hh;  <<<<<< uninitialized pointer, value is garbage
>    printf("abc\n"); free(hh); printf("def\n");
> }
> 
> int main()
> { // If the following printf statement is commented out
>    // then no error message ("Exiting due to signal SIGSEGU")
> 
>    printf("calling test\n");

It has nothing to do with `printf' per se: simply, a call to `printf'
allocates some memory internally, and then the garbage in hh is
different, so it causes a crash.