error C2065: Undeclared Identifier

[jamez05]

I'm using Visual Studio 2005 on Windows XP. I'm trying to compile a C program. I'm down to one error. When I try to compile the following, I get the error:

initmol.c(20) : error C2065: 'NULL' : undeclared identifier

Here's the code. It errors out on the IF statement:

#include <malloc.h>
#include "molecule.h"

MOLECULE *InitMol( void )
{
   MOLECULE *m;
	
 
   if ( (m = (MOLECULE *)malloc( sizeof( *m ) )) == NULL ) {
	  return( NULL );
   }

   m->N_Hydro = -1;
   m->N_Atoms =  0;
   m->N_Bonds =  0;
   m->N_Comps =  0;
   return( m );
}

 

[cpjust]

I guess malloc.h doesn't define NULL. Try including <stddef.h>

 

[jamez05]

Thanks cpjust.

I ended up replacing malloc.h with stdio.h and got rid of the malloc cast and it solved the problem:

#include <stdio.h>
#include "molecule.h"

MOLECULE *InitMol( void )
{
   MOLECULE *m;
    
 
   if ( (m = (MOLECULE *)sizeof( *m ) ) == NULL ) {
      return( NULL );
   }

   m->N_Hydro = -1;
   m->N_Atoms =  0;
   m->N_Bonds =  0;
   m->N_Comps =  0;
   return( m );
}

 

[cpjust]

Well now you aren't allocating any memory at all. You're just setting the pointer to the size of the MOLECULE struct. This will blow up when you run it.

 

[jamez05]

Thanks cpjust, that's exactly what's happening. I will
change it back and add <stddef.h>. I'll let you know what happens

 

[ArkM]

The NULL macro and malloc func are both declared in <stdlib.h>.