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Editorial Team
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Asked: 2026-05-15T14:34:46+00:00

This may look like a trivial problem. Sorry in that case, I am not

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This may look like a trivial problem. Sorry in that case, I am not able to find the actual way. I understand that automatic variable are un-initilaized. So a code snippet provided below is likely to dump in block-2 

char *p;  
if(NULL == p)  
{  
   //do something  block-1 statement
}  
else  
{  
  //do something else  block-2 statement
}

Now, in most of the platform the default value of the automatic variable is either 0 or NULL especially SUSE Linux flavours.

Question

a. Is there any compiler flag or any other option which will force the setting up of local variable to a “junk” value if un-initialized?

PS : I know that static analyzer tool will be easily able to detect the problem. I just wanted to know if this can be done at run time also through some flags/option setting.

I am using SUSE 10/HP-UX and AIX platforms.

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1 Answer

  1. Editorial Team

    What you see here is an artifact of how memory is usually allotted to processes on Unix.

    Since the stack segment is not stored in the disk-file image of the executable the OS has to allocate new pages to the stack at program start. These come as zero-filled initially, same as the .bss. This initial zero-filling of the stack is historical. There was an attempt to “simplify” it to not do that. Too many programs broke, so the move was abandoned.

    Run your program for a while, make multiple function calls, – you’ll see “junk” on the stack eventually 🙂

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