This document provides a guide through the major capabilities of the GNAT Programming System by working on a code example: sdc, a simple desktop calculator.
It is important to realize that the features that you are about to experiment with are available on multiple platforms, using the same user interface and capabilities, providing a user-friendly environment with a tight integration between the tools.
Start GPS in the directory containing the tutorial files, or if the directory
is read-only, copy the tutorial directory and its subdirectories in a
local (writable) area, and start GPS from the tutorial directory, so
that GPS will load the right context.
By default, the tutorial sources can be found under
<prefix>/doc/gps/examples/tutorial, where <prefix> is the
prefix directory of the GPS installation.
Alternatively, if you have already started GPS in another directory, you
can load the project sdc.gpr by using the menu Project->Open...
Having launched GPS, you should now have access to a main window composed of several areas:
In the project explorer, open the common directory by clicking
on the [+] sign on the left of common.
This will open the directory and display a list of source files located
in this directory.
Now, double click on sdc.adb: this will open a source editor on this
file. The source code is syntax-highlighted: keywords, comments, strings and
characters have different colors.
As with many other properties, colors are configurable in GPS:
Select the menu Edit->Preferences. This will open a preferences
dialog window.
Select the Editor->Fonts & Colors page by clicking on the cross next to
the item Editor and then selecting the Fonts & Colors item.
As you go over the various lines and labels, you will notice that by holding the mouse over a label, a tool tip pops up displaying on-line help about the selected item.
Change the background color of the Keywords by clicking on the last
down arrow, at the right of the Keywords line.
Choose a color, e.g a light green. When you're done with the color selection, simply click again on the arrow.
Click on the Apply button and look at the effects in the source
editor. If you like the new display, click on OK to confirm the
changes, otherwise clicking on Cancel will revert to the previous
color.
Select the menu Build->Make->sdc.adb: this will launch a complete
build of the sdc application. Note also that a key binding
is associated with this menu item (<F4>).
The build has generated a number of errors in a new window: the Locations tree, displayed in the bottom area. The errors are also highlighted in the corresponding source editor.
GPS has automatically jumped to the first error message (sdc.adb, 28:6 : (style) bad indentation), at the line (28) and column (06) of the error.
Fix the error by hand by inserting a space.
Now you can fix the next error by moving the cursor to the line 30 (press the <down> arrow twice), and by using <Ctrl-Tab> (press first the <Control> key, and then the <Tab> key on your keyboard): this key combination asks the source editor to automatically re-indent the current line.
Note that on some window managers or desktop environments,
<Ctrl-Tab> is already defined. If this is the case, you can change this
shortcut from the key shortcuts dialog (menu Edit->Key shortcuts,
Source editor section, Format selection item).
You can then fix all the remaining errors by selecting the whole block (from line 28 to line 40) and pressing <Ctrl-Tab>. To select a block, you can either click on the left mouse button and select the area while holding the button, or using the keyboard by pressing the <Shift> key and moving the cursor using the <Up> or <Down> keys.
Press the <F4> key to build again. GPS will automatically save the modified files, and start a build. This behavior (automatic saving of files before building) can be configured in the preferences dialog.
If you look at the bottom right of the GPS window, you will notice that a progress bar has appeared, displaying the current number of files compiled, and the number of remaining files.
This should now report a successful build.
Now let's try to understand a little bit about how the program is working by
looking at the sdc.adb editor: there's a loop, the main processing is
done by the functions Process and Next (at line 30).
Click around line 30, move the mouse over Process and let a tool tip
appear (global procedure tokens.process declared at tokens.ads:19): this
gives information about the kind of entity and the location (file and line) of
the declaration of this procedure, as well as documentation for this function,
as extracted from the comments surrounding the procedure declaration.
Do the same for Next (global function tokens.next declared at
tokens.ads:15).
Keeping the mouse over Next, display the contextual menu by clicking on
the right mouse button,
then click on Goto declaration of Next: we're now in the package
Tokens, in file tokens.ads; but where is this file in the project?
Select the menu Navigate->Find or Replace...: this will open a search
dialog.
In the Search for: text entry type tokens.ads. Then
select Project explorer in the Look in: area. The search
area provides an easy way to search for text or regular expressions in
several contexts including the current file, the project explorer, ...
Now click on Find. The file tokens.ads, in directory struct
is highlighted.
Close the search dialog by clicking on the Close button.
Note that in this specific case, a simpler way to locate a file in the
explorer is to use the contextual menu from the source editor:
Locate in explorer: tokens.ads.
Click on the [+] sign to open tokens.ads entities.
When you click on a file in the explorer, you get
language sensitive information about the file, such as
packages, subprograms, tasks, ... for Ada.
Open the subprogram category, click on Process: this
will open tokens.ads and move the cursor on the first line
corresponding to the procedure Process.
Similarly, click on Next, and move your mouse on Next
in the source editor.
Using the contextual menu, select Goto body of Next;
scroll through the procedure Next, move the mouse on
Instructions.Read at line 46 and from the contextual menu, select
Goto body of Read.
We've now navigated quite a bit through the application source code, which you can verify by clicking on the left arrow in the tool bar, to go back to the previous locations visited.
Repeat the operation until you're back in sdc.adb.
As with the undo/redo capability in the source editor, the
goto previous/next location is infinite.
It is now time to run the application: select the menu
Build->Run->sdc, which will open a dialog window.
Type input.txt in the text entry: this is the name of a text
file that will be passed as argument to the sdc program.
Now click on OK: a new window titled Run: sdc input.txt
is created at the bottom of the main window where the sdc application
runs and displays an unexpected internal error: this is a good opportunity
to use the integrated debugger.
Close the execution window by clicking on the x icon on the top right corner of this window.
Open the preferences dialog (menu Edit->Preferences) and
click on the Debugger item on the left; set the button
Break on exceptions to Enabled: this will enable by default a special
breakpoint every time an exception is raised. Click on OK to confirm your
change.
Now select the menu Debug->Initialize->sdc: two new windows are
created, a data window and a debugger console.
You can also look at the various debug menu item and tool bar buttons which are
now activated.
Use the menu Debug->Data->Call Stack: this opens a new window on the
right of the source editors. If you select the contextual menu in the call
stack, various pieces of information can be displayed or
removed in the call stack. From this contextual menu, add the
Frame Number info by clicking on it.
Now select the menu Debug->Run.... Notice that input.txt has
been filled automatically for you since the two menus Build->Run... and
Debug->Run... are synchronized. Click on OK: the debugger should
stop on an exception (Constraint_Error in the file stack.adb, at
line 49).
Go up in the call stack by clicking on the tokens.process line
(frame number 6).
If you move the mouse over the parameter T at line 64, a tool tip is
displayed showing the value of T. You have probably noticed that
tool tips, like menus, are contextual: depending on the current session and
on the entity selected, different information is displayed.
Select the contextual menu Debug->Display T: this displays in the data
window a box containing the different fields of T, each clearly
separated.
On T data display, select the contextual menu
Display->Show Value + Type: this displays for all fields both their
type and value.
Special colors are used in the data display: blue for pointers that can be
dereferenced by a double-click (double click on T.val); red for fields
that have been modified since last step.
In the contextual menu that pops up when you hold the mouse over T.
select Debug->View memory at address of T: a memory view is opened.
Use the up and down arrows on the right to visit memory.
Click in the memory dump, and modify it by typing numbers. Notice the
red color for modified values;
click on Undo Changes to cancel the modifications;
click on Close to close the memory window.
In the call stack, go back to stack.push frame (num 4).
Move the mouse over Last and let the debugger display its value: 0.
From the contextual menu, select Goto declaration of Last: this
will jump to the line 16 of stack.adb, where you can see that
Last is a Natural. Now click on the Goto Previous Location
button in the tool bar: we're now back at line 49 where we can see that for a
Push procedure, Last should be incremented, and not decremented.
Fix the line to Last := Last + 1;
Save the file (<Ctrl-S>);
End the debug session: menu Debug->Terminate;
Rebuild (press <F4> key);
Rerun (menu Build->Run->sdc): the program now completes as expected.
Close the execution window.
Now go back to the file sdc.adb, move the mouse over the procedure
sdc at line 8, select the contextual menu
References->Sdc calls: this will open a new window titled
Call graph browser.
Click on the right arrow of Process (one of the first items on
the right). Also click on the right arrow of error_msg.
Select Orthogonal links in the contextual menu of the graph to change the
way links are displayed in the graph.
You may then play with the zoom (<=> and <-> keys).
If you select Hide links from error_msg contextual menu, this
will hide all the links that are related to this item: the link between the
callers and callees of error_msg are no longer displayed. This can
be useful when the graph becomes complex, to hide some parts. If you go back to
the contextual menu, you can now select Show links to show the links
again.
Click on right arrow of process ((Decl) instructions.ads:12).
The items can also be moved: move e.g msg item around.
Click on left arrow of msg
to display who is calling msg. Notice that view (on the left
of the graph) calls msg.
Click on left arrow of view: the arrow disappears, and no
new items are created, which means that view isn't called by anyone,
so we're now going to remove this procedure.
From view, click on the blue link: stack.ads:32, this will open
the file stack.ads at line 32.
Then from the source editor (file stack.ads), select the contextual
menu References->Find all references to View: this highlights the
Locations tree which now contains all the references for view,
grouped by files (stack.ads and stack.adb).
The first location is highlighted automatically: this is the spec of the
procedure View. Now click in the tree on the + sign at the left
of stack.adb: two locations are listed, at line 90 and 97.
Click on each of these locations: they correspond to the procedure body.
The Find all references capability is another way to list all the uses of
an entity, and it confirms that View isn't called in our project.
Remove View body by e.g selecting it, and pressing the <Delete> key, then save the file (<Ctrl-S>).
Do the same for the spec, save the file.
Close the stack.ads and stack.adb files (menu File->Close,
or using the shortcut <Ctrl-W>), as well as the call graph window.
Rebuild by pressing the <F4> key.
Let's now see how to create a project corresponding to the sdc project we've used in this tutorial.
Go to the menu Project->New...: this is a standard wizard, with various
steps listed on the left area of the window.
The first page of the wizard allows you to select what kind of project you
want to build, depending on the information you have. Select the default
choice Single Project, and press Forward.
Type sdc2 in the project name field.
Click on Forward: we are now on the language selection page.
It is possible to create a multi-language project by e.g. selecting the C or C++
check box.
Click on Forward: we are now on the VCS page. VCS stands
for Version Control System.
GPS provides a generic framework for VCS which allows it to support
new systems easily. Systems supported by default are CVS, ClearCase and
Subversion. Select CVS.
Click on Forward: this is the source directories selection,
used to specify the project's sources. Click on the Add button,
and select the struct directory, then click on OK to validate.
Click on Forward: this is the Build and Exec directory
selection, used to store object, ali files, ...
Click on Browse, then click on obj, and finally click on
OK.
Click on Forward: this is the main units selection, used mainly for
building executables and debugging.
Click on Add, open the common directory and select
sdc.adb.
Click on Forward: this is the naming scheme editor.
GNAT is very flexible and can use any kind of naming scheme for Ada files.
In particular, you can easily set the default file
extensions (e.g by using one of the predefined schemes) and you
can also specify exceptions that use non standard file names.
Click on Forward: we're now in the switch selector.
Select Recompile if switches changed.
Click on Ada page.
Select Full errors and Overflow checking.
The boxes and the command line (the text entry at the
bottom of the page) are fully synchronized, e.g if you click on the
command line, and change -gnatf to -gnat, the
Full errors check box is unselected; now type a to get
-gnata, and notice that Enable assertions is now selected.
Click on Forward: voila, we've created a project similar to the one
used in this tutorial.
Click on Cancel to close the wizard.
In the project explorer, on the project sdc, use the contextual menu
Edit project->Properties.
All the properties set in the project wizard can be found here as well.
You can switch between pages by clicking on the tabs located along the
left side of the window.
Once you're done exploring the property pages, click on the Cancel
button to close the properties window.
Select the menu Tools->Scenario View. This will add a new window in
GPS, which contains a Build label.
This is a configuration variable. With GPS and the GNAT project facility, you can define as many configuration variables as you want, and modify any project settings (e.g. switches, sources, ...) based on the values of configuration variables. These variables can also take any number of different values.
The Build variable demonstrates a typical Debug/Production
configuration where we've set different switches for the two modes.
Click on the button at the left (Edit variable properties): this
is the variable editor, where values can be added or renamed.
Close the variable editor by clicking on the Cancel button.
Now, let's take a look at the switches set in the project.
Select the menu item Project->Edit File Switches: a global
switch editor is displayed in the working area, showing the
switches associated with each file in the sdc project.
The editor lists the switches associated with each file in the project.
Gray entries indicate default (global) switches. Notice that
screen_output.adb has specific switches, which are highlighted
using a different font.
Switch between Debug and Production mode in the Build
combo box: the switches are updated automatically.
Back to our project, let's now examine the dependencies between sources.
Select sdc.adb in the explorer and then the contextual menu item
Show dependencies for sdc.adb: this will open a new graph showing
the dependencies between sources of the project.
Click on the right arrow of tokens.ads to display the files that
tokens.ads depends on. Similarly, click on the right arrow of
stack.ads.
Back in the project explorer, on the Sdc project, select the contextual
menu Edit project->Dependencies, then on the Add From File,
then open the tutorial
directory and click on the projects subdirectory. Select the file
prj1.gpr. Click on Apply to validate the change.
You can see the new dependency added in the project explorer, as a tree of
projects. In particular, project dependencies are duplicated: if you open
the prj1 icon by clicking on the [+] sign, and then
similarly open the prj2 icon, you will notice that the project
prj4 is displayed twice: once as a dependency of prj2, and
once as a dependency of prj1.
GPS can also display the graph of dependencies between projects: on Sdc
project, use the contextual menu
Show projects imported by Sdc: this will open a project hierarchy
browser.
On the Sdc.gpr project, select the contextual menu
Show projects imported by Sdc recursively.
In the browser, you can move the project items, and select them to highlight the dependencies.
Close the project browser by clicking on the [x] sign at the top right
area of the window, or by typing <Ctrl-W>, or by using the menu
File->Close.
This terminates our tour of GPS, the GNAT Programming System. We hope this tutorial gave you a good overview of the general capabilities available with GPS. A non exhaustive list of the features not mentioned in this document includes:
For more information, please look at the User's Guide (<gps.html>).