A critical feature of a debugger is the ability to see the current values of variables, and to change those values when necessary. This ability allows you to understand the details of your program's execution, and to experiment with new possibilities.

This section discusses the following topics:

• Viewing local variables
• Viewing global variables
• Placing data in a new window
• Viewing data types
• Viewing data in a different format
• Viewing data as different types
• Changing the value of a variable
• Using the Expressions window
• Viewing raw memory
• Viewing memory at an address
• Viewing Processor Registers

Local variables are displayed in the Variables pane of the Thread window (Figure 11.60). If the variable is a handle, pointer, or structure, you can click the hierarchical control to the left of the name to expand the view. This allows you to see the members of the structure, or the data referenced by the pointer or handle.

To learn some useful tips for using hierarchical controls, see "Expanding and Collapsing Groups". For more information about the Variables pane of the Thread window, refer to "Variables pane."

To view global variables, open the Global Variables window. Use one of the following techniques:

• (Windows menu bar layout) Choose View > Global Variables Window.
• (Macintosh menu bar layout) Choose Window > Global Variables Window.

For more information, see "Global Variables Window".

Sometimes the Variables pane and Global Variables window are not the most convenient places to view data. You can place any variable or group of variables in a separate window.

To place a variable or memory location in its own window, double-click its name (Figure 11.62) or select the name and choose Data > View Variable, or choose the View Variable command from the debugger contextual menu (Figure 11.18). If the variable is an array, use the View Array command instead. To view the memory the variable occupies as a memory dump, use either the View Memory or View Memory As command.

For more information, see "Variable Window," "Array Window," and "Memory Window".

If you wish, the debugger can display the data types of variables on a window-by-window basis. Select the window or pane in which you want data types displayed and choose Data > Show Types, or choose the Show Types command from the debugger contextual menu (Figure 11.18). Then, the relevant data type follows the names of the variables and memory locations in that window or pane (Figure 11.63).

To show data types automatically, enable the following preference in the Display Settings preference panel of the IDE Preferences window:

In variable panes, show variable types by default

See "Display Settings" for more information.

You display a variable's value in several formats:

• binary
• signed decimal
• unsigned decimal
• hexadecimal
• character
• C string
• Pascal string
• unicode string
• floating point
• enumeration
• Fixed
• Fract

Not all formats are available for all data types. For example, if a variable is an integral value (such as type short or long), you can view it in signed decimal, unsigned decimal, hexadecimal, character, or string format. However, you cannot view the same variable in floating-point, Fixed, or Fract format.

The View As command in the Data menu lets you change the data type in which a variable, register, or memory value appears:

1. Select the item in a window or pane.

2. Choose Data > View As.

Alternatively, you can use the debugger contextual menu (Figure 11.18) to select the same command. After you choose the View As menu command, the debugger displays the View As dialog box, shown in Figure 11.65.

3. Select the data type by which to view the item.

The data type you select is displayed in the New Type text field near the bottom of the dialog box. If you want to treat the item as a pointer, append an asterisk (*) to the type name.

4. Click OK.

The display of the item's value changes to the specified type.

You can change the value of a variable in any variable view. Variables are displayed in several debugging windows: the Variables pane of the Thread window or Symbolics window, a Variable window, an Array window, or the Expressions window. To change the value, double-click the variable (or select it and press Enter/Return) and type the new value (Figure 11.66).

You can enter variable values in any of the following formats:

• decimal
• hexadecimal
• floating point
• C string
• Pascal string
• character constant
Changing a Variable Value:

The Expressions window provides a single place to put frequently used local variables, global variables, structure members, array elements, and complex expressions. To open this window, use one of the following techniques:

• (Windows menu bar layout) Choose View > Expressions.
• (Macintosh menu bar layout) Choose Window > Expressions Window.

The IDE updates the contents of the Expressions window whenever execution stops in the debugger. The IDE leaves blank any variable that is out of scope. You can use the Expressions window to perform a number of tasks:

For more information, see "Expressions Window".

To examine and change the raw contents of memory:

1. Select an item or expression representing the base address of the memory you want to examine.

2. Choose Data > View Memory.

A new Memory window opens and displays the contents of memory in hexadecimal and ASCII format. You can change memory directly from the Memory window by entering hexadecimal values or characters. You can also change the beginning address of the memory being displayed by changing the expression in the Display text field at the top of the window.

The View Memory and View Memory As commands in the Data menu allow you to follow any pointer-including an address stored in a register-and view the memory to which it currently points.

To display the memory referenced by a pointer, follow these steps:

1. Select the value of the variable or register in a window in which it appears.

2. Choose Data > View Memory or Data > View Memory As.

If you choose the View Memory menu command, stop with this step. A Memory window opens and displays a raw memory dump, starting at the address referenced by the pointer.

If you choose the View Memory As menu command, continue to the next step. A dialog box (Figure 11.67) opens and prompts you to select a data type.

3. If you chose Data > View Memory As, select a data type in the View As dialog box.

The data type you select appears in the New Type field. To view the memory pointed to by a register, append an asterisk (*) to the type name.

4. Click OK in the View As dialog box.

A new window opens (Figure 11.68) and displays the contents of memory, starting at the address referenced by the pointer.

For more information, refer to "Memory Window".

To view the contents of the processor's general registers, choose Window > Registers Windows > General Registers (Figure 11.69).

For more information, see "Register Windows".