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Default variable assignment

Started by Leadorn Jun 13, 2002 at 4:23 AM 6 replies 400+ views

Original Post

Jun 13, 2002 at 4:23 AM

Hail I have done some writing to file test, and I have discovered that my unsigned char variable on creation gets assigned with 0xdc. Why wasn''t my unsigned variable assigned 0x00? Is there an technical explanation for this, or is it the compiler?

Grul

Jun 13, 2002 at 4:34 AM

Unintialized variables or pointers always get the value 0xCDCDCD... etc in Windows. That is why you should always initialize your variables before you use them. Initialize them to 0 if you don''t know which value it is going to have at the moment.

Leadorn

Author

Leadorn

Jun 13, 2002 at 4:38 AM

Why did they choose 0xdc?

I use this code to create a variable to 500 byte array, how do I assign them all to NULL the easiest way?

    
unsigned char *he = new unsigned char [500];

[edited by - leadorn on June 13, 2002 5:55:03 AM]

felonius

Jun 13, 2002 at 4:56 AM

use the standard library function memset().

siaspete

Jun 13, 2002 at 5:11 AM

Note that they only get 0xCD in Debug builds, so you can easily see uninitialised memory. In Release they get whatever was in memory previously.

Helpful links:
How To Ask Questions The Smart Way | Google can help with your question | Search MSDN for help with standard C or Windows functions

Leadorn

Author

Leadorn

Jun 13, 2002 at 6:30 AM

mkay

That make sense, using it as debug tool.

DarkEmpire

Jun 13, 2002 at 6:31 AM

Instead of using memset, you can use your own initialisation function:

http://www.hailstorm.net/papers/smallwin32.htm#buffer

here is the content for ZeroMemory:



#ifdef FillMemory
#undef FillMemory
#endif
#ifdef ZeroMemory
#undef ZeroMemory
#endif



__forceinline 
void FillMemory(void *dest,unsigned __int8 c,unsigned __int32 count)
{
	unsigned __int32	size32=count>>2;
	unsigned __int32	fill=(c<<24|c<<16|c<<8|c);
	unsigned __int32	*dest32=(unsigned __int32*)dest;

	switch( (count-(size32<<2)) )
	{
	case 3:	((unsigned __int8*)dest)[count - 3] = c;
	case 2:	((unsigned __int8*)dest)[count - 2] = c;
	case 1:	((unsigned __int8*)dest)[count - 1] = c;
	}

	while( size32-- > 0 )
		*(dest32++) = fill;

}  /* FillMemory */

#define ZeroMemory(dest,count) FillMemory(dest,0,count)

Leadorn

Author

Leadorn

Jun 13, 2002 at 12:11 PM

Mkay thanks guys and girls.

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