Errata for Advanced CORBA Programming with C++ (4th Printing)

Last updated: 28 January 2004

Acknowledgments

A number of people have submitted comments, constructive criticism, and feedback since the first printing. Our thanks go to everyone who helped us weed out bugs and make this a better book. All the people who contributed are listed in the acknowledgments to our readers.

Chapter 3

• Pages 44 and 45

  The code to check the number of arguments should follow the call to ORB_init instead of preceding it. This is necessary if additional ORB-specific options are passed on the commmand line.

Chapter 4

• Page 74

  The members of type Adata and Bdata of the ABunion are swapped. The union definition should read:

  union ABunion switch (StructType) {
  case A_TYPE:
      struct Acontents {
          Adata                   data;
          sequence<ABunion, 1>    nested; // Contained Bdata
      } A_member;
  case B_TYPE:
      struct Bcontents {
          Bdata                   data;
          sequence<ABunion, 1>    nested; // Contained Adata
      } B_member;
  };
  

• Pages 117 and 118

  The second repository identifier in the list near the top of the pages is shown as IDL:CCS/Tempttype:1.0. It should be IDL:CCS/TempType:1.0.

Chapter 6

• Page 200

  The call to StrArray_copy on the third-last line of the code example passes the address of the array instead of the array itself. The call should read:

  StrArray_copy(x, sp1);  // Copy contents of sp1 into x
  

• Pages 212 and 214

  The return type of operator[] is incorrect. The operators return a reference to the element type of the sequence (not the sequence type itself). Assuming an element type TE, the correct declarations are:

        TE & operator[](CORBA::ULong);       // For sequences
  const TE & operator[](CORBA::ULong) const; // For sequences
  

• Page 217

  The first sentence of the section Additional T_var Member Functions for Fixed-Length Types should read:

  For a T_var for a fixed-length structure or union of type T, the IDL compiler generates the following:

• Page 218

  The return type T & of the T_var assignment operator is incorrect. The correct signature is:

  T_var & operator=(const T &)
  

Chapter 7

• Pages 240 and 241

  The code example to illustrate incorrect use of down-casts uses incorrect types. The example should read:

  CCS::Thermostat_ptr tmstat = ...;   // Get reference
  CORBA::Object_ptr o = tmstat;       // OK
  CCS::Thermostat_ptr tmstat2;
  
  tmstat2 = dynamic_cast<CCS::Thermostat_ptr>(o);     // Bad!
  tmstat2 = static_cast<CCS::Thermostat_ptr>(o);      // Bad!
  tmstat2 = reinterpret_cast<CCS::Thermostat_ptr>(o); // Bad!
  tmstat2 = (CCS::Thermostat_ptr)o;                   // Bad!
  
  tmstat2 = CCS::Thermostat::_narrow(o);              // OK
  

• Page 262

  The second code example has the variable p in the wrong scope. The example should read:

  CCS::Thermometer_ptr p = ...;   // Get reference
  {
      CCS::Thermometer_var v;
      v = p;                      // v takes ownership
      // Use v...
  } // No leak here - v's destructor calls
    // release and p now dangles.
  

• Page 276

  The operation name in the IDL example at the bottom of the page should be long_op instead of op_long.

• Page 292

  The type definition for Varr_slice should read:

  typedef Vls Varr_slice;
  

• Page 294

  The IDL at the top of the page should read:

  interface Foo {
      Foo ref_op(
              in Foo    ref_in,
              inout Foo ref_inout,
              out Foo   ref_out
      );
  };
  

• Pages 297-299

  The C++ mapping for _var types is under-specified in CORBA 2.3 because it does not show how _var types for fixed-length underlying types should work. On 10 January 2000, the OMG C++ Mapping RTF voted to clarify the situation by specifying the mapping for _var types for fixed-length underlying types. (Note that the implementation shown is not binding in the sense that its internals may differ in each ORB; however, the semantics must be the same.) The upshot of this mapping is that, once initialized (which is always via a deep copy), a _var variable for a fixed-length underlying type behaves like a value of the underlying type.

• Pages 308 and 309

  The BadTemp exception is used with the wrong scoped name. The correct scope is CCS::Thermostat::BadTemp.

• Page 312

  The example code tries to down-cast a system exception to a BadTemp exception, which cannot possibly work. The correct code is:

  try {
      tmstat_ref->set_nominal(500);
  } catch (const CORBA::Exception & e) {
      // Check what sort of exception it is...
      const CORBA::SystemException * se;
      const CCS::Thermostat::BadTemp * bt;
      if (se = CORBA::OBJECT_NOT_EXIST::_downcast(&e)) {
          // It is an OBJECT_NOT_EXIST exception
      } else if (bt = CCS::Thermostat::BadTemp::_downcast(&e)) {
          // It is a BadTemp exception
      } else {
          // It is some other exception
      }
      // Do not deallocate se here -- the exception
      // still owns the memory pointed to by se or bt.
  }
  

• Page 313

  The example code tries to down-cast a system exception to a BadTemp exception, which cannot possibly work. The correct code is:

  try {
      tmstat_ref->set_nominal(500);
  } catch (const CORBA::Exception & e) {
      // Check what sort of exception it is...
      const CORBA::SystemException * se;
      const CCS::Thermostat::BadTemp * bt;
      if (se = dynamic_cast<const CORBA::OBJECT_NOT_EXIST *>(&e)) {
          // It is an OBJECT_NOT_EXIST exception
      } else if (bt =
              dynamic_cast<const CCS::Thermostat::BadTemp *>(&e)) {
          // It is a BadTemp exception
      } else {
          // It is some other exception
      }
  }
  

Chapter 9

• Page 362

  The first definition in the code example should read:

  const int array_length = sizeof(Darr)/sizeof(*Darr);
  

• Page 371

  The first definition in the second code example should read:

  const int array_length = sizeof(Varr)/sizeof(*Varr);
  

• Page 376

  The declaration of the set_nominal function uses the wrong scope for the BadTemp exception. The correct declaration is:

  virtual CCS::TempType set_nominal(CCS::TempType new_tmpe)
      throw(CORBA::SystemException, CCS::Thermostat::BadTemp) = 0;
  

• Page 377

  The BadTemp exception is used with the wrong scoped name in three places. The correct scope is CCS::Thermostat::BadTemp.

• Page 380/381

  The code example deletes the previously allocated vls_out pointer and then throws an exception without changing the pointer value. This is a grey area in the C++ mapping: it is not clear whether the skeleton will attempt to delete the value of an out parameter when an exception is thrown. (Currently, we are aware of skeleton implementions that call delete on the parameter when an exception is thrown and others that do not.)

  To make the code portable for either kind of skeleton implementation, it is necessary to set the vls_out argument to zero before throwing the exception:

  catch (const CORBA::Exception &) {
      delete vls_out.ptr();
      vls_out = 0;		// Required for portability
      delete result;
      throw;
  }
  

  The same situation arises for inout parameters, which also need to be set to zero before throwing an exception.

  Note that there is no need to set the return value to zero for either kind of skeleton implementation.

  Instead of writing code such as the example on page 380/381, we recommend that you use a _var type to hold an allocated out or inout parameter and call its _retn member function once no more exceptions can be thrown, as shown on page 381/382. This is both simpler and correct for either kind of skeleton implementation.

Chapter 10

• Page 407

  The StrFinder function contains a memory leak. The two calls to strcmp should read:

  return strcmp(CORBA::String_var(p.second->location()), m_str) == 0;
  

  and

  return strcmp(CORBA::String_var(p.second->model()), m_str) == 0;
  

  The same error appears on page 417.

Chapter 11

• Page 447

  The IDL definitions for the AdapterAlreadyExists and InvalidPolicy exceptions should be in the scope of the POA interface.

• Page 463

  The IDL definitions for the ServantAlreadyActive, ObjectAlreadyActive, and WrongPolicy exceptions should be in the scope of the POA interface.

• Page 467

  The call to activate_object incorrectly passes the servant instead of the address of the servant. The call should read:

  poa->activate_object(&ctrl_servant);

• Page 505

  The transition labelled F should be deleted from the diagram and the transition table.

• Page 506

  The description in the second paragraph talks about POAs, when it should be talking about POAManagers instead. Destruction of a POAManager is automatic and occurs when the last POA using the POAManager is destroyed.

• Page 519

  The code example makes a number of calls to find_POA and then activates the POA manager. However, the POA manager is created in the holding state, so the calls to find_POA will not be dispatched and the code deadlocks.

  To fix the problem, the statements

  // Activate our POAManager.
  PortableServer::POAManager_var mgr = root_poa->the_POAManager();
  mgr->activate();
  

  must be moved to precede the calls to find_POA.

Chapter 12

• Pages 582 and 583

  The call to push_front(oid) at the end of the incarnate function should precede the instantiation of the new servant.

Chapter 13

• Page 611

  The third paragraph following the IDL example states:

  Note that the size of the structure CD in Figure 13.2 is 13 bytes...

  This should read:

  Note that the size of the structure CD in Figure 13.2 is 14 bytes...

• Page 625

  The last line states that the components field is used only by IIOP 1.1. This is incorrect; the components field is used by both IIOP 1.1 and IIOP 1.2.

Chapter 16

• Page 703

  The member_name accessor is missing a parameter declaration. It should read:

  const char * member_name(ULong index) const;
  

• Page 720

  The final three statements of the code example incorrectly use >> instead of >>= for extraction. They should read:

  foo_any >>= foo_p;      // Succeeds
  aof_any >>= foo_p;      // Succeeds in 2.3, undefined in 2.2
  bar_any >>= foo_p;      // Fails in 2.3, undefined in 2.2
  

• Page 730

  The type code for the Node structure is correct, but TypeCode::equal does not return true when comparing this type code to the _tc_Node type code that is generated by the IDL compiler. (Only TypeCode::equivalent returns true for the comparison.)

  To get TypeCode::equal to return true when comparing the struct_tc in the example with the generated _tc_Node type code, the second-last statement of the example should read:

  members[1].type = orb->create_sequence_tc(0, rec_tc);
  

Chapter 18

• Page 785

  The first two sentences of the second paragraph should read:

  resolve_initial_references cannot return a nil reference, unless someone has misconfigured the ORB.

Chapter 17

• Page 760

  The example code requires an additional call at the end:

  error_msg->destroy();
  

Chapter 19

• Page 838

  The final paragraph says that

  The Address property has the type code Manufacturing::_tc_AddressType.

  This should read

  The Manufacturer property has the type code Manufacturing::_tc_AddressType.

• Page 852

  The code to create a service type for the controller uses property modes that disagree with the ones shown in Table 19.1 on page 838 for the Supports and MaxDevices properties. The code for these two properties should read:

  props[3].name = CORBA::string_dup("Supports");
  props[3].value_type = CORBA::TypeCode::_duplicate(
                          Airconditioning::_tc_ModelType
                        );
  props[3].mode = ServiceTypeRepository::PROP_READONLY;
  
  props[4].name = CORBA::string_dup("MaxDevices");
  props[4].value_type = CORBA::TypeCode::_duplicate(
                          CORBA::_tc_ulong
                        );
  props[4].mode = ServiceTypeRepository::PROP_NORMAL;
  

• Page 885

  The expression near the bottom of the page is missing a * operator and should read:

  min(12.3 * mem_size + 4.6 * file_size)

• Page 902

  The final line of the first bullet point mentions the limiting_follow_policy. This should read limiting_follow_rule instead.

Chapter 21

• Page 975

  The second paragraph states that even for requests made locally, they must be dispatched on the POA's single thread instead of the caller's thread.

  Different ORB vendors have interpreted the wording in the specification differently, so the semantics of the SINGLE_THREAD_MODEL policy with respect to collocated calls are currently under discussion. Until this matter is settled in the OMG Core Revision Task Force, you must assume that it is implementation-dependent whether the call is dispatched on the POA's single thread or the caller's thread.

• Page 993

  The implementation of preinvoke should include a call to servant->_add_ref() before returning, and postinvoke should include a corresponding call to servant->_remove_ref(). These calls are necessary to ensure that the servant remains in existence for the duration of the operation.

Appendix A

• Page 1026

  The implementation of ICP_set does not always correctly NUL-terminate the location string. The correct implementation is:

  extern "C"
  int
  ICP_set(unsigned long id, const char * attr, const void * value)
  {
      // Look for id in state map
      StateMap::iterator pos = dstate.find(id);
      if (pos == dstate.end())
          return -1;                          // No such device
  
      // Change either location or nominal temp, depending on attr.
      if (strcmp(attr, "location") == 0) {
          pos->second.location = (const char *)value;
      if (pos->second.location.size() >= MAXSTR)
          pos->second.location[MAXSTR - 1] = '\0';
      } else if (strcmp(attr, "nominal_temp") == 0) {
          if (pos->second.type != thermostat) 
              return -1;                      // Must be thermostat
          short temp;
          memcpy(&temp, value, sizeof(temp));
          if (temp < MIN_TEMP || temp > MAX_TEMP)
              return -1;
          pos->second.nominal_temp = temp;
      } else {
          return -1;                          // No such attribute
      }
      return 0;                               // OK
  }
  

• Page 1028

  The implementation of ~ICP_Persist does not always correctly NUL-terminate the location string. A call to c_str is missing in the loop that writes the device attributes:

  db << i->second.location.c_str() << endl;
  

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