Viewing Variables, Members, Types, and Classes

dbx's whatis command prints the declarations or definitions of identifiers, structs, types and C++ classes, or the type of an expression. The identifiers you can look up include variables, functions, fields, arrays, and enumeration constants.

Looking Up Definitions of Variables, Members, and Functions

To print out the declaration of an identifier:

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(dbx) whatis identifier

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Qualify the identifier name with file and function information as needed.

To print out the member function

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(dbx) whatis block::draw
void block::draw(unsigned long pw);
(dbx) whatis table::draw
void table::draw(unsigned long pw);
(dbx) whatis block::pos 
class point *block::pos();
Notice that table::pos is inherited from block:
(dbx) whatis table::pos
class point *block::pos();

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To print out the data member:

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(dbx) whatis block::movable
int movable;

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On a variable, whatis tells you the variable`s type:

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(dbx) whatis the_table
class table *the_table;

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On a field, whatis tells you the field`s type:

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(dbx) whatis the_table->draw
void table::draw(unsigned long pw);

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When you are stopped in a member function, you can lookup the this pointer. In this example, the output from the whatis shows that the compiler automatically allocated this variable to a register.

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(dbx) stop in brick::draw
(dbx) cont
// expose the blocks window (if exposed, hide then expose) to force program to hit the breakpoint.
(dbx) where 1
brick::draw(this = 0x48870, pw = 374752), line 124 in
     "block_draw.cc"
(dbx) whatis this
class brick *this;

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Looking Up Definitions of Types and Classes

To print the declaration of a type or C++ class:

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(dbx) whatis -t type_or_class_name

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To see inherited members the whatis command takes an option -r (for recursive) that displays the declaration of a specified class together with the members it inherits from parent classes.

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(dbx) whatis -t -r  class_name

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The output from a whatis -r query may be long, depending on the class hierarchy and the size of the classes. The output begins with the list of members inherited from the most ancestral class. Note the inserted comment lines separating the list of members into their respective parent classes.

Here are two examples, using the class table, a child class of the parent class load_bearing_block, which is, in turn, a child class of block.

Without -r, whatis reports the members declared in class table:

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(dbx) whatis -t class table
class table : public load_bearing_block {
public:
    table::table(char *name, int w, int h, const class point &pos);
    virtual char *table::type();
    virtual void table::draw(unsigned long pw);
};

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Here are results when whatis -r is used on a child class to see members it inherits

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(dbx) whatis -t -r class table
class table : public load_bearing_block {
public:
  /* from base class table::load_bearing_block::block */
  block::block();
  block::block(char *name, int w, int h, const class point &pos, class
load_bearing_block *blk);
    virtual char *block::type();
    char *block::name();
    int block::is_movable();
//  deleted several members from exampleprotected:
    char *nm;
    int movable;
    int width;
    int height;
    class point  position;
    class load_bearing_block *supported_by;
    Panel_item panel_item;
    /* from base class table::load_bearing_block */
public:
 load_bearing_block::load_bearing_block();
 load_bearing_block::load_bearing_block(char *name, int w, int h,
const class point &pos, class load_bearing_block *blk);
    virtual int load_bearing_block::is_load_bearing();
    virtual class list *load_bearing_block::supported_blocks();
    void load_bearing_block::add_supported_block(class block &b);
    void load_bearing_block::remove_supported_block(class block &b);
    virtual void load_bearing_block::print_supported_blocks();
    virtual void load_bearing_block::clear_top();
 virtual void load_bearing_block::put_on(class block &object);
    class point load_bearing_block::get_space(class block &object);
    class point load_bearing_block::find_space(class block &object);
    class point load_bearing_block::make_space(class block &object);
protected:
    class list *support_for;
    /* from class table */
public:
    table::table(char *name, int w, int h, const class point &pos);
    virtual char *table::type();
    virtual void table::draw(unsigned long pw);
};

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