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strcmp core dumps

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# 1  
Old 02-21-2006
strcmp core dumps
hi everyone,

Right now when I do:

strcmp(s1, s2);

i get a core dump because at times s1 or s2 can be nothing so that makes strcmp() core dump.

What is the solution, if at times I expect one of them (or both) to be NULL?
I want to be able to compare that s1 is NULL and s2 is "blah" or whatever.
My point is to know whenever these 2 differ.

any ideas?
# 2  
Old 02-21-2006
Though not pretty (and not fully correct)

Code:
strcmp ( ( s1 ? s1 : "" ), ( s2 ? s2 : "" ) );

Something like this would be a bit more graceful:

Code:
    int             Differ;


    if ( s1 == NULL || s2 == NULL )
    {
        if ( s1 == s2 )
        {
            Differ = 0;
        }
        else
        {
            Differ = 1;
        }
    }
    else
    {
        Differ = strcmp (s1, s2);
    }

    if ( Differ ) ...

# 3  
Old 02-21-2006
Quote:
Originally Posted by hegemaro
Though not pretty (and not fully correct)

Code:
strcmp ( ( s1 ? s1 : "" ), ( s2 ? s2 : "" ) );

Something like this would be a bit more graceful:

Code:
    int             Differ;


    if ( s1 == NULL || s2 == NULL )
    {
        if ( s1 == s2 )
        {
            Differ = 0;
        }
        else
        {
            Differ = 1;
        }
    }
    else
    {
        Differ = strcmp (s1, s2);
    }

    if ( Differ ) ...


thanks, was hoping there would be a more "correct" way to do this.
I really thought this would be a more common problem with a lib function I could use in this case. But thanks much for your solution, if all else fails, I may have to use that.
# 4  
Old 02-21-2006
Perhaps you misunderstood me, the single line was not fully correct -- it can not tell the difference between a NULL and a zero-length string. The larger chunk of code with the Differ boolean is fully correct.
# 5  
Old 02-21-2006
Quote:
Originally Posted by hegemaro
Perhaps you misunderstood me, the single line was not fully correct -- it can not tell the difference between a NULL and a zero-length string. The larger chunk of code with the Differ boolean is fully correct.
right, what I meant was I was hoping I could use something like strncmp() instead that would know how to treat NULL...etc..

thanks again though, I think your latter suggestion is the way I'll have to go.
# 6  
Old 02-22-2006
Barfing on a NULL pointer is actually the desired behavior.

Merely having a zero length string won't be a problem for strcmp. The mian cause for this is that you are missing the "trailing" nul character in a string.

If the strcmp occurs in the function where a and b are declared otherwise pass in sizoef(a) and sizeof(b) as arguments:
Code:
#define BARADRG -256
/* strcmp -- strncmp can't return a minus 256 */
if(a!=NULL && b!=NULL)
{
      result=strncmp(a,b, ( sizeof(a)>sizeof(b) )? sizeof(a):sizeof(b));
}
else
      result=BADARG;
}

# 7  
Old 02-26-2006
My obsessive-compulsiveness is shining through. Combing both Jim's post and mine, we can get a "null strcmp" function that is comparable to the strcmp library function in performance.

It is identical to the Solaris strcmp function returning the ordinal difference between the first pair of non-matching bytes. (As I recall, the AIX implementation returns a 0 for a match and 1 for a non-match). This function returns -256 if S1 is NULL, 256 if S2 is NULL, and 0 if both S1 and S2 are NULL.


Code:
    int nstrcmp ( void * S1 , void * S2 )
    {
        if ( S1 == NULL )
        {
            S2 = ( S2 ? (void *) 256 : S2 );
        }
        else if ( S2 == NULL )
        {
            S1 = (void *) 256;
        }
        else
        {
            unsigned char * s1 = (unsigned char *) S1,
                          * s2 = (unsigned char *) S2;
   

            while ( *s1 )
            {
                if ( *s1 != *s2 )
                {
                    break;
                }
                s1++;
                s2++;
            }

            return ( (int) (*s1 - *s2) );
        }

        return ( (int) (S1 - S2) );
    }

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