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Unfortunately, const-qualified objects cannot be used where compile-time integer constants are required, namely to define the

• size Size of a bit-field member of a structure.
• size Size of an array (except in the case of variable length arrays).
• value Value of an enumeration constant.
• value Value of a case constant.

If any of these are required, then an integer constant (which would be an rvalue) must be used.

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Object-like macros do not consume memory, and, ; consequently, it is not possible to create a pointer to one. Macros do not provide for type checking because they are textually replaced by the preprocessor.

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#ifndef PORTNUMBER     /* Might be passed on compile line */
#  define PORTNUMBER 1234
#endif

#ifndef HOSTNAME        /* Might be passed on compile line */
#  define HOSTNAME "localhost"
#endif

/* ... */

LDAP *ld = ldap_init(HOSTNAME, PORTNUMBER);
if (ld == NULL) {
  perror("ldap_init");
  return(1);
}

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Using numeric literals makes code more difficult to read and understand. Buffer overruns are frequently a consequence of a magic number being changed in one place (like such as in an array declaration) but not elsewhere (like such as in a loop through an array).

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