OpenVMS Debugger Manual

Supported constructs in language and address expressions for C++ follow:

Symbol	Construct
[ ]	Subscripting
. (period)	Structure component selection
->	Pointer dereferencing
::	Scope resolution

C.7.3 Data Types

Floating-point numbers of type float may be represented by F_Floating or IEEE S_Floating, depending on compiler switches.

Floating-point numbers of type double may be represented by IEEE T_Floating, D_Floating, or G_Floating, depending on compiler switches.

C.7.4 Case Sensitivity

Symbol names are case sensitive in C++. This means that uppercase and lowercase letters are treated as different characters.

C.7.5 Displaying Information About a Class

Use the command SHOW SYMBOL to display static information about a class declaration. Use the command EXAMINE to view dynamic information about class objects (see Section C.7.6).

The command SHOW SYMBOL/FULL displays the class type declaration, including:

Data members (including static data members)
Member functions (including static member functions)
Constructors and destructors
Base classes and derived classes

For example:

dbg> SHOW SYMBOL /TYPE C type C struct (C, 13 components), size: 40 bytes overloaded name C instance C::C(void) instance C::C(const C &) dbg> SHOW SYMBOL /FULL C type C struct (C, 13 components), size: 40 bytes inherits: B1, size: 24 bytes, offset: 0 bytes B2, size: 24 bytes, offset: 12 bytes contains the following members: overloaded name C::g instance C::g(int) instance C::g(long) instance C::g(char) j : longword integer, size: 4 bytes, offset: 24 bytes s : longword integer, size: 4 bytes, address: # [static] overloaded name C int ==(C &) C & =(const C &) void h(void) [virtual] ~C(void) __vptr : typed pointer type, size: 4 bytes, offset: 4 bytes __bptr : typed pointer type, size: 4 bytes, offset: 8 bytes structure has been padded, size: 4 bytes, offset: 36 bytes overloaded name C instance C::C(void) instance C::C(const C &) DBG>

Note that SHOW SYMBOL/FULL does not display members of base classes or derived classes. Use the commands SHOW SYMBOL/FULL base_class_name and SHOW SYMBOL/FULL derived_class_name to display information about members of those classes. For example:

DBG> SHOW SYMBOL /FULL B1 type B1 struct (B1, 8 components), size: 24 bytes inherits: virtual A is inherited by: C contains the following members: i : longword integer, size: 4 bytes, offset: 0 bytes overloaded name B1 void f(void) B1 & =(const B1 &) void h(void) [virtual] __vptr : typed pointer type, size: 4 bytes, offset: 4 bytes __bptr : typed pointer type, size: 4 bytes, offset: 8 bytes structure has been padded, size: 12 bytes, offset: 12 bytes overloaded name B1 instance B1::B1(void) instance B1::B1(const B1 &) DBG>

Use the command SHOW SYMBOL/FULL class_member_name to display information about class members. For example:

DBG> SHOW SYMBOL /FULL j record component C::j address: offset 24 bytes from beginning of record atomic type, longword integer, size: 4 bytes record component A::j address: offset 4 bytes from beginning of record atomic type, longword integer, size: 4 bytes DBG>

Use the SHOW SYMBOL/FULL command to display detailed information about an object.

Note that SHOW SYMBOL does not currently support qualified names. For example, the following commands are not currently supported:

SHOW SYMBOL object_name.function_name SHOW SYMBOL class_name::member_name

C.7.6 Displaying Information About an Object

The debugger uses C++ symbol lookup rules to display information about objects. Use the command EXAMINE to display the current value of an object. For example:

DBG> EXAMINE a CXXDOCEXAMPLE\main\a: struct A i: 0 j: 1 __vptr: 131168 DBG>

You can also display individual object members using the member access operators, period (.) and right arrow (->), with the EXAMINE command. For example:

DBG> EXAMINE ptr CXXDOCEXAMPLE\main\ptr: 40 DBG> EXAMINE *ptr *CXXDOCEXAMPLE\main\ptr: struct A i: 0 j: 1 __vptr: 131168 DBG> EXAMINE a.i CXXDOCEXAMPLE\main\a.i: 0 DBG> EXAMINE ptr->i CXXDOCEXAMPLE\main\ptr->i: 0 DBG>

The debugger correctly interprets virtual inheritance. For example:

DBG> EXAMINE c CXXDOCEXAMPLE\main\c: struct C inherit B1 inherit virtual A i: 8 j: 9 __vptr: 131200 i: 10 __vptr: 131232 __bptr: 131104 inherit B2 inherit virtual A (already printed, see above) i: 11 __vptr: 131280 __bptr: 131152 j: 12 __vptr: 131232 __bptr: 131104 DBG>

Use the scope resolution operator (::) to reference global variables, to reference hidden members in base classes, to explicitly reference a member that is inherited, or otherwise to name a member hidden by the current context. For example:

DBG> EXAMINE c.j CXXDOCEXAMPLE\main\c.j: 12 DBG> EXAMINE c.A::j CXXDOCEXAMPLE\main\c.A::j: 9 DBG> EXAMINE x CXXDOCEXAMPLE\main\x: 101 DBG> EXAMINE ::x CXXDOCEXAMPLE\x: 13 DBG>

To resolve ambiguous member references, the debugger lists the members that satisfy the reference and requests an unambiguous reference to the member. For example:

DBG> EXAMINE c.i %DEBUG-I-AMBIGUOUS, 'i' is ambiguous, matching the following CXXDOCEXAMPLE\main\c.B1::i CXXDOCEXAMPLE\main\c.B2::i %DEBUG-E-REENTER, reenter the command using a more precise pathname DBG> EXAMINE c.B1::i CXXDOCEXAMPLE\main\c.B1::i: 10 DBG>

Use the scope resolution operator (::) to refer to static data members. For example:

DBG> EXAMINE c.s CXXDOCEXAMPLE\main\c.s: 42 DBG> EXAMINE C::s C::s: 42 DBG>

Use the SHOW SYMBOL/FULL to display the class type of an object (see Section C.7.5).

C.7.7 Setting Watchpoints

You can set watchpoints on objects. All nonstatic data members are watched (including those in base classes). Static data members are not watched when you set a watchpoint on the object. However, you can explicitly set watchpoints on static data members. For example:

DBG> SET WATCH c %DEBUG-I-WPTTRACE, non-static watchpoint, tracing every instruction DBG> GO watch of CXXDOCEXAMPLE\main\c.i at CXXDOCEXAMPLE\main\%LINE 50+8 50: c.B2::i++; old value: 11 new value: 12 break at CXXDOCEXAMPLE\main\%LINE 51 51: c.s++; DBG> SET WATCH c.s DBG> GO watch of CXXDOCEXAMPLE\main\c.s at CXXDOCEXAMPLE\main\%LINE 51+16 51: c.s++; old value: 43 new value: 44 break at CXXDOCEXAMPLE\main\%LINE 53 53: b1.f(); DBG>

C.7.8 Debugging Functions

The debugger uses C++ symbol lookup rules to display information on member functions. For example:

DBG> EXAMINE /SOURCE b1.f module CXXDOCEXAMPLE 14: void f() {} DBG> SET BREAK B1::f DBG> GO break at routine B1::f 14: void f() {} DBG>

The debugger correctly interprets references to the this pointer. For example:

DBG> EXAMINE this B1::f::this: 16 DBG> EXAMINE *this *B1::f::this: struct B1 inherit virtual A i: 2 j: 3 __vptr: 131184 i: 4 __vptr: 131248 __bptr: 131120 DBG> EXAMINE this->i B1::f::this->i: 4 DBG> EXAMINE this->j B1::f::this->A::j: 3 DBG>EXAMINE i B1::f::this->i: 4 DBG> EXAMINE j B1::f::this->A::j: 3 DBG>

The debugger correctly references virtual member functions. For example:

DBG> EXAMINE /SOURCE %LINE 53 module CXXDOCEXAMPLE 53: b1.f(); DBG> SET BREAK this->h DBG> SHOW BREAK breakpoint at routine B1::f breakpoint at routine B1::h !! !! We are at the call to B1::f made at 'c.B1::f()'. !! Here this->h matches C::h. !! DBG> GO break at routine B1::f 14: void f() {} DBG> EXAMINE /SOURCE %LINE 54 module CXXDOCEXAMPLE 54: c.B1::f(); DBG> SET BREAK this->h DBG> SHOW BREAK breakpoint at routine B1::f breakpoint at routine B1::h breakpoint at routine C::h !! !! Handling overloaded functions !! DBG> show symbol/full g overloaded name C::g routine C::g(char) type signature: void g(char) address: 132224, size: 128 bytes routine C::g(long) type signature: void g(long) address: 132480, size: 96 bytes DBG> SET BREAK g %DEBUG-I-NOTUNQOVR, symbol 'g' is overloaded overloaded name C::g instance C::g(int) instance C::g(long) instance C::g(char) %DEBUG-E-REENTER, reenter the command using a more precise pathname DBG> SET BREAK g(int) DBG> CANCEL BREAK/ALL DBG>

If you try to set a break on an overloaded function, the debugger lists the instances of the function and requests that you specify the correct instance. For example, with Debugger Version 7.2:

DBG> SET BREAK g %DEBUG-I-NOTUNQOVR, symbol 'g' is overloaded overloaded name C::g instance void g(int) instance void g(long) instance void g(char *) %DEBUG-E-REENTER, reenter the command using a more precise pathname DBG> SET BREAK g(int) DBG>

The debugger provides support for debugging constructors, destructors, and operators. For example:

DBG> SET BREAK C %DEBUG-I-NOTUNQOVR, symbol 'C' is overloaded overloaded name C instance C::C(void) instance C::C(const C &) %DEBUG-E-REENTER, reenter the command using a more precise pathname DBG> SHOW SYMBOL /FULL ~C routine C::~C type signature: ~C(void) code address: #, size: 152 bytes procedure descriptor address: # DBG> SET BREAK ~C DBG> SET BREAK %NAME'==' %DEBUG-W-UNALLOCATED, '==' is not allocated in memory (optimized away) %DEBUG-E-CMDFAILED, the SET BREAK command has failed DBG> SHOW SYMBOL /FULL ==, routine c::operator==, type signature: bool operator==© code address: 198716, size: 40 bytes, procedure descriptor address: 65752 DBG> SET BREAK operator== DBG> SHOW SYMBOL /FULL == routine C::== type signature: int ==(C &) address: unallocated DBG> SHOW BREAK breakpoint at routine C::~C DBG> DBG> examine C::~C C::~C: alloc r35 = ar.pfs, 3F, 01, 00 DBG> DBG> ex/source ~C module CXXDOCEXAMPLE 37: ~C() {}

C.7.9 Limitations on Debugger Support for C++

The following limitations apply when you debug a C++ program:

• You cannot specify a template by name in a debugger command. You must use the name of the instantiation of the template.
• In C++, expressions in the instantiated template name can be full constant expressions, such as stack<double,f*10>. This form is not yet supported in the debugger; you must enter the value of the expression (for example, if f is 10 in the stack example, you must enter 100).

Example C-1 contains CXXDOCEXAMPLE.C, a C++ example program.

Example C-1 C++ Example Program CXXDOCEXAMPLE.C

int x = 0; struct A { int i,j; void f() {} virtual void h() {}; A() { i=x++; j=x++; } }; struct B1 : virtual A { int i; void f() {} virtual void h() {} B1() { i=x++; } }; struct B2 : virtual A { int i; void f() {} virtual void h() {} B2() { i=x++; } }; struct C : B1, B2 { int j; static int s; void g( int ) {} void g( long ) {} void g( char ) {} void h() {} operator ==( C& ) { return 0; } C() { j=x++; } ~C() {} }; int C::s = 42; main() { A a; B1 b1; B2 b2; C c; A *ptr = &a; int x = 101; x++; c.s++; c.B2::i++; c.s++; b1.f(); c.B1::f(); c.g(1); c.g( (long) 1 ); c.g( 'a' ); }

Example C-2 contains a sample debugging session of the program contained in Example C-1.

Example C-2 C++ Debugging Example

DBG> GO break at routine CXXDOCEXAMPLE\main 44: A a; B1 b1; B2 b2; C c; DBG> STEP stepped to CXXDOCEXAMPLE\main\%LINE 45 45: A *ptr = &a; DBG> STEP stepped to CXXDOCEXAMPLE\main\%LINE 46 46: int x = 101; DBG> STEP stepped to CXXDOCEXAMPLE\main\%LINE 47 47: x++; !! !! Displaying class information !! DBG> SHOW SYMBOL /TYPE C type C struct (C, 13 components), size: 40 bytes overloaded name C instance C::C(void) instance C::C(const C &) DBG> SHOW SYMBOL /FULL C type C struct (C, 13 components), size: 40 bytes inherits: B1, size: 24 bytes, offset: 0 bytes B2, size: 24 bytes, offset: 12 bytes contains the following members: overloaded name C::g instance C::g(int) instance C::g(long) instance C::g(char) j : longword integer, size: 4 bytes, offset: 24 bytes s : longword integer, size: 4 bytes, address: # [static] overloaded name C int ==(C &) C & =(const C &) void h(void) [virtual] ~C(void) __vptr : typed pointer type, size: 4 bytes, offset: 4 bytes __bptr : typed pointer type, size: 4 bytes, offset: 8 bytes structure has been padded, size: 4 bytes, offset: 36 bytes overloaded name C instance C::C(void) instance C::C(const C &) !! !! Displaying information about base classes !! DBG> SHOW SYMBOL /FULL B1 type B1 struct (B1, 8 components), size: 24 bytes inherits: virtual A is inherited by: C contains the following members: i : longword integer, size: 4 bytes, offset: 0 bytes overloaded name B1 void f(void) B1 & =(const B1 &) void h(void) [virtual] __vptr : typed pointer type, size: 4 bytes, offset: 4 bytes __bptr : typed pointer type, size: 4 bytes, offset: 8 bytes structure has been padded, size: 12 bytes, offset: 12 bytes overloaded name B1 instance B1::B1(void) instance B1::B1(const B1 &) !! !! Displaying class member information !! DBG> SHOW SYMBOL /FULL j record component C::j address: offset 24 bytes from beginning of record atomic type, longword integer, size: 4 bytes record component A::j address: offset 4 bytes from beginning of record atomic type, longword integer, size: 4 bytes !! !! Simple object display !! DBG> EXAMINE a CXXDOCEXAMPLE\main\a: struct A i: 0 j: 1 __vptr: 131168 !! !! Using *, -> and . to access objects and members !! DBG> EXAMINE ptr CXXDOCEXAMPLE\main\ptr: 40 DBG> EXAMINE *ptr *CXXDOCEXAMPLE\main\ptr: struct A i: 0 j: 1 __vptr: 131168 DBG> EXAMINE a.i CXXDOCEXAMPLE\main\a.i: 0 DBG> EXAMINE ptr->i CXXDOCEXAMPLE\main\ptr->i: 0 !! !! Complicated object example !! DBG> EXAMINE c CXXDOCEXAMPLE\main\c: struct C inherit B1 inherit virtual A i: 8 j: 9 __vptr: 131200 i: 10 __vptr: 131232 __bptr: 131104 inherit B2 inherit virtual A (already printed, see above) i: 11 __vptr: 131280 __bptr: 131152 j: 12 __vptr: 131232 __bptr: 131104 !! !! The debugger using C++ symbol lookup rules (to match c.j) !! and then the use of :: to specify a particular member named j. !! DBG> EXAMINE c.j CXXDOCEXAMPLE\main\c.j: 12 DBG> EXAMINE c.A::j CXXDOCEXAMPLE\main\c.A::j: 9 !! !! Using the global scope resolution operator. !! DBG> EXAMINE x CXXDOCEXAMPLE\main\x: 101 DBG> EXAMINE ::x CXXDOCEXAMPLE\x: 13 !! !! Handling ambiguous member references. !! DBG> EXAMINE c.i %DEBUG-I-AMBIGUOUS, 'i' is ambiguous, matching the following CXXDOCEXAMPLE\main\c.B1::i CXXDOCEXAMPLE\main\c.B2::i %DEBUG-E-REENTER, reenter the command using a more precise pathname DBG> EXAMINE c.B1::i CXXDOCEXAMPLE\main\c.B1::i: 10 !! !! Refering to static data members: with . and with :: !! DBG> EXAMINE c.s CXXDOCEXAMPLE\main\c.s: 42 DBG> EXAMINE C::s C::s: 42 !! !! Setting watchpoints on objects. All non-static data members !! are watched (including those in base classes). Static data !! members are not watched. Of course watchpoints on static data !! members can be set explicitly. !! DBG> SET WATCH c %DEBUG-I-WPTTRACE, non-static watchpoint, tracing every instruction DBG> GO watch of CXXDOCEXAMPLE\main\c.i at CXXDOCEXAMPLE\main\%LINE 50+8 50: c.B2::i++; old value: 11 new value: 12 break at CXXDOCEXAMPLE\main\%LINE 51 51: c.s++; DBG> SET WATCH c.s DBG> GO watch of CXXDOCEXAMPLE\main\c.s at CXXDOCEXAMPLE\main\%LINE 51+16 51: c.s++; old value: 43 new value: 44 break at CXXDOCEXAMPLE\main\%LINE 53 53: b1.f(); !! !! Basic member lookup applies to functions. !! DBG> EXAMINE /SOURCE b1.f module CXXDOCEXAMPLE 14: void f() {} DBG> SET BREAK B1::f DBG> GO break at routine B1::f 14: void f() {} !! !! Support for 'this'. !! DBG> EXAMINE this B1::f::this: 16 DBG> EXAMINE *this *B1::f::this: struct B1 inherit virtual A i: 2 j: 3 __vptr: 131184 i: 4 __vptr: 131248 __bptr: 131120 DBG> EXAMINE this->i B1::f::this->i: 4 DBG> EXAMINE this->j B1::f::this->A::j: 3 DBG>EXAMINE i B1::f::this->i: 4 DBG> EXAMINE j B1::f::this->A::j: 3 !! !! Support for virtual functions. !! !! We are at the call to B1::f made at 'b1.f()'. !! Here this->h matches B1::h. !! DBG> EXAMINE /SOURCE %LINE 53 module CXXDOCEXAMPLE 53: b1.f(); DBG> SET BREAK this->h DBG> SHOW BREAK breakpoint at routine B1::f breakpoint at routine B1::h !! !! We are at the call to B1::f made at 'c.B1::f()'. !! Here this->h matches C::h. !! DBG> GO break at routine B1::f 14: void f() {} DBG> EXAMINE /SOURCE %LINE 54 module CXXDOCEXAMPLE 54: c.B1::f(); DBG> SET BREAK this->h DBG> SHOW BREAK breakpoint at routine B1::f breakpoint at routine B1::h breakpoint at routine C::h !! !! Handling overloaded functions !! DBG> SET BREAK g %DEBUG-I-NOTUNQOVR, symbol 'g' is overloaded overloaded name C::g instance C::g(int) instance C::g(long) instance C::g(char) %DEBUG-E-REENTER, reenter the command using a more precise pathname DBG> SET BREAK g(int) DBG> CANCEL BREAK/ALL !! !! Working with constructors, destructors, and operators. !! DBG> SET BREAK C %DEBUG-I-NOTUNQOVR, symbol 'C' is overloaded overloaded name C instance C::C(void) instance C::C(const C &) %DEBUG-E-REENTER, reenter the command using a more precise pathname DBG> SHOW SYMBOL /FULL ~C routine C::~C type signature: ~C(void) code address: #, size: 152 bytes procedure descriptor address: # DBG> SET BREAK %NAME'~C' DBG> SET BREAK %NAME'==' %DEBUG-W-UNALLOCATED, '==' is not allocated in memory (optimized away) %DEBUG-E-CMDFAILED, the SET BREAK command has failed DBG> SHOW SYMBOL /FULL == routine C::== type signature: int ==(C &) address: unallocated DBG> SHOW BREAK breakpoint at routine C::~C DBG> EXIT