labwindows nullChk returns with an error

Question

What is nullChk and how should it be properly used?

I am using the following line of code:

nullChk(temp = malloc (numBytes + 1));  

and I get the following error message:

  700, 9    error: use of undeclared identifier 'error'
  700, 9    error: use of undeclared label 'Error'

Answer 1

It looks like nullChk is a macro. I found the definition and comment below in toolbox.h. Note the assumptions that are listed. You don't have to use this macro if you don't want to -- I find it unnecessary myself.

/*  The errChk and nullChk macros are useful for implementing a consistent error
    handling system.  These can macros can be place around function calls to
    force an  automatic jump to a function's error handling code when an error 
    occurs.  This is analogous to exception handling, and is even easier to use.

    These macros make the following assumptions:
        1)  The following local declaration of an error code variable is
            made in every function in which they are used:

            int error = 0;

        2)  Every function in which they are used contains a goto label
            named Error which precedes the error handling code for the function.

        3)  Every function call or error code enclosed in a errChk() macro
            is assumed to return an integer which, if negative, is the code for
            the error which occured.  If the value is zero or positive then the
            error checking macros have no effect.

            Every function call or value enclosed in a nullChk() macro is
            assummed to return a non-zero value if no error occurred, or a
            zero value if an "Out Of Memory" error occurred (nullChk() is
            useful for malloc, calloc, and similar resource allocation functions).
*/

#ifndef errChk
#define errChk(fCall) if (error = (fCall), error < 0) \
{goto Error;} else
#endif

#ifndef nullChk
#define nullChk(fCall) if ((fCall) == 0) \
{error = UIEOutOfMemory; goto Error;} else
#endif

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