C Macros

C Macros

Ctalk also provides many macros that help standardize the Ctalk-to-C conventions. They’re defined in the ctalkdefs.h include file. To use them, include ctalkdefs.h in a source file or class library.

#include <ctalk/ctalkdefs.h>

Some of the macro definitions in ctalkdefs.h are described here.

ARG

With a numeric argument, retrieves the n’th method or template argument from the stack; i.e., ARG(0) refers to the first argument on the stack, ARG(1) retrieves the second argument, and so on.

CLASSNAME

Returns an object’s classname.

Note: You should use this macro in new code. While typing __o_classname directly with an OBJECT * should work for a while, it’s going to be phased out.

Using __o_classname with an object and the -> method is still okay, though. For example:

  OBJECT *myObjRef;
  String new myString;

  /* The use of __o_classname as struct member is going away... */
  myObjRef -> __o_classname;
  /* Instead, write this. */
  myObjRef -> CLASSNAME;

  /* These are still okay, because -> is a method, not the C operator. */
  myString -> __o_classname;
  self -> __o_classname;

  /* The same is true for the SUPERCLASSNAME definition. */

  SUPERCLASSNAME(myObjRef);

  self -> SUPERCLASSNAME;
  myString ->  SUPERCLASSNAME;

FILEEOF

Writes an fEOF to the char * buffer given as its argument.

FMT_0XHEX

When used with a function like sprintf (), formats a pointer into its string representation. For example:

char buf[64];
OBJECT *my_object_ptr;

....   /* Do stuff. */

sprintf (buf, FMT_0XHEX(my_object_ptr));

However, this macro is not very portable and using functions that use stdargs (e.g., printf, scanf, etc.) can be cumbersome. Library functions like __ctalkGenericPtrFromStr () See ctalkGenericPtrFromStr, and __ctalkFilePtrFromStr () See ctalkFilePtrFromStr, might be faster and more reliable.

IS_OBJECT

Returns True or False if its argument, a C pointer, refers to a valid object.

IS_VALUE_INSTANCE_VAR

Returns True or False if its argument, a C pointer, refers to the value instance variable of an object.

MEMADDR

Casts its operand to a void **, which is what Ctalk’s internal function __xfree () uses when freeing memory. Normally you should use __ctalkFree () to free memory, but the MEMADDR macro is here in case you want to call __xfree () directly. Refer to the entry for __ctalkFree () for details. See ctalkFree.

STR_0XHEX_TO_PTR

Does the converse of FMT_0XHEX; it converts the string representation of a pointer into an actual pointer, when used with a function like sscanf (). For example:

OBJECT *my_object;
OBJECT *my_object_ptr;

sscanf (my_object -> __o_value, STR_0XHEX_TO_PTR(my_object_ptr));

Again, using stdargs functions can be cumbersome and not very portable. In many cases, __ctalkObjValPtr () accomplishes the same thing. See ctalkObjValPtr.

SUPERCLASSNAME

Returns an object’s superclass name. This macro should be used only with OBJECT *’s, as it is rather extensive and written in C. Returns an empty string if the object doesn’t have a superclass. See CLASSNAMEMacro, above.

__LIST_HEAD(List *l)

When given an argument that is a collection like a List object, returns the first member of the collection.

STR_IS_NULL(char *s)

Evaluates to True if the char * argument evaluates to zero; i.e., its value is ‘(null)’, ‘0’, ‘0x0’ or the first character is an ASCII NUL (‘\0’) byte.