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Replace the old data window by the Debugger Variables view. Change-Id: I44b1e81593efa738df8d94178382388563c0b648
69 lines
3.3 KiB
ReStructuredText
69 lines
3.3 KiB
ReStructuredText
*****
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Debug
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*****
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Open the preferences dialog (menu `Edit->Preferences...`) and click on the
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`Debugger` item on the left; set the button `Break on exceptions` to *Enabled*:
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this will enable by default a special breakpoint every time an exception is
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raised. Click on `Close` to close dialog.
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Now click on the `Build & Debug sdc.adb` toolbar button: GNAT Studio
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automatically switches to the *Debug* perspective as shown in the menu
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`Window->Perspectives`, and new windows have appeared: the variables window,
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the breakpoints view and the debugger console at the bottom, and the call
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stack window on the right.
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You can also look at the various debug menu item and tool bar buttons which are
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now activated.
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On the call stack window (you can use the menu `Debug->Data->Call Stack` to
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open it if you do not have it displayed), select the local configuration menu:
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various pieces of information can be displayed or removed in the call stack.
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From this local configuration menu, add the `Frame Number` info by clicking on
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it.
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Now click on the `Debug continue` button and type `input.txt` in the text input
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field. Check that 'Stop at beginning of main subprogram' and 'Use exec dir
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instead of current dir' are not selected. Click on `OK`: the debugger should
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stop on an exception (`Constraint_Error` in the file :file:`stack.adb`, at line
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49).
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Go up in the call stack by clicking on the `tokens.process` frame (frame number
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will vary, depending on your GNAT version and platform).
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If you move the mouse over the parameter `T` at line 64, a tool tip is
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displayed showing the value of `T`. You have probably noticed that tool tips,
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like menus, are contextual: depending on the current session and on the entity
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selected, different information is displayed.
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Select the contextual menu `Debug->Display T`: this will open the
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`Debugger Variables` view, displaying graphically the contents of the different
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fields of `T`, each clearly separated.
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Special colors are used in the data display depending on your theme: one
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for pointers that can be dereferenced by a double-click (double click
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on `T.val`); another one for fields that have been modified since last step.
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From the T box, right-click to display the contextual menu and select `View
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memory at address of T`: a memory view is opened on top of the source editors.
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Use the `up` and `down` arrows on the right to visit memory.
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Click in the memory dump, and modify it by typing numbers. Notice the red color
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for modified values; click on `Undo Changes` to cancel the modifications; then
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close the memory window by e.g. clicking on the `x` icon in the tab or pressing
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:kbd:`Ctrl-W`.
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In the call stack, go back to the `stack.push` frame. Move the mouse
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over `Last` and let the debugger display its value: 0. From the contextual
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menu, select `Goto declaration of Last`: this will jump to the line 16 of
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:file:`stack.adb`, where you can see that `Last` is a `Natural`. Now click on
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the `Goto Previous Location` button in the tool bar: we're now back at line 49
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where we can see that for a `Push` procedure, `Last` should be incremented, and
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not decremented.
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Fix the line to `Last := Last + 1;`
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Save the file (:kbd:`Ctrl-S`); End the debug session: `Debug terminate` toolbar
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button; Rebuild (press :kbd:`F4` key); Rerun (menu `Build->Run->sdc`, click on
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`Execute`): the program now completes as expected. Close the execution window.
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