global variable turns zero

I have a Windows console application. And I have declared few global variable.
Found while debugging, this global( i.e. RunFlag) variable becomes 0 while execution sscanf function.

Code:

---

BYTE RunFlag;

if ( sscanf( p+4,"%02X%03X",&Id,&frequency) != 2 )

---

where frequency is global variable and Id is local.

Can anybody help and tell why this weird this happening

Can you post a bit more code (a small, compilable section that shows the problem)

If RunFlag is being changes indirectly, it's probably due to an overflow somewhere (at a guess).

If its not to hard, try rewriting the code without the use of global variables. You can pass locals with the const modifier to make sure they are not changed. Const is not supported on all systems though, so watch out.

Code:

---

BYTE RunFlag;
INT16 frequency;

BYTE foo(BYTE *p)
{
        BYTE Id,error = 0;
       
        // Get the ID and frequency from command string
if ( sscanf( p+4,"%02X%03X",&Id,&frequency) != 2 )  RunFlag is origionally1
//and turn 0 here
        {
                ERROR(error = 10);
                return error;
        }

---

where frequency and RunFlag is global variables and Id is local.

Do you think that it is problem with sscanf function.

I don't see anything obviously wrong there. More debugging, I'm afraid ;)

What is ERROR ?

Try to pinpoint the exact location the variable changes. Add a load of :
>printf ("RunFlag %d\n", RunFlag);
statements to the code

I you still can't get it, break the code down into smaller chunks and go from there.

If you want help, post something on here that we can compile and run.

Thanks for everybody

Salems's post helped me to resolve the peoblem.

But I want to clarify one thing, do you means that all pointer that I pass to sscanf must point to 32 bit number.

As I am developing this application in VC++, I looked as MSDN and example is as follow

Code:

---

#include <stdio.h>

void main( void )
{
  char  tokenstring[] = "15 12 14...";
  char  s[81];
  char  c;
  int  i;
  float fp;

  /* Input various data from tokenstring: */
  sscanf( tokenstring, "%s", s );
  sscanf( tokenstring, "%c", &c );
  sscanf( tokenstring, "%d", &i );
  sscanf( tokenstring, "%f", &fp );

  /* Output the data read */
  printf( "String    = %s\n", s );
  printf( "Character = %c\n", c );
  printf( "Integer:  = %d\n", i );
  printf( "Real:    = %f\n", fp );
}

---

this does not require content of pointer to be 32 bit. If that is the case, don't you think is limitation of sscanf?

please let me know