Tag Archives: C++

Pretty printing C++ with Clang-Format

I use some of the code generation and refactoring tools in QtCreator. These save a lot of time, but they don’t format C++ code how I like it. For example they produce C++ code like this:

void MyClass::foo(int *x)

But I like my code formatted like this:

void MyClass::foo( int* x )

The differences may seem minor, but they are a source of significant irritation to me. I like my code how I like it, goddammit! And consistent formatting enhances readability. However re-formatting it by hand is time-consuming and tedious.

What I need is a tool that can enforce consistent formatting in the style that I like, or something close. I have tried to use automatic C++ formatting (pretty printing) tools in the past, but I couldn’t get them to produce a format that was close enough to what I wanted. But I have finally found the tool for the job. Clang-Format.

Clang-Format is part of the LLVM family of tools. It is a free, command-line tool that reformats C++, Objective-C or C according to the settings in a config file. As with many free tools, it isn’t terribly well documented. Some of the documentation on the web is out of date and some of it is incomplete. But I have managed to find out enough to configure it how I like it.

To run it you just need to place your options in a .clang-format file, make sure the clang-format executable is in the path and then run it:

clang-format.exe -i -style=file <C++ file>

Here are the settings I am currently using in my .clang-format file:

Language: Cpp
AccessModifierOffset: -4
AlignAfterOpenBracket: false
AlignConsecutiveAssignments: false
AlignConsecutiveDeclarations: false
AlignEscapedNewlinesLeft: false
AlignOperands: true
AlignTrailingComments: false
AllowAllParametersOfDeclarationOnNextLine: false
AllowShortBlocksOnASingleLine: false
AllowShortCaseLabelsOnASingleLine: false
AllowShortFunctionsOnASingleLine: Inline
AllowShortIfStatementsOnASingleLine: false
AllowShortLoopsOnASingleLine: false
AlwaysBreakAfterDefinitionReturnType: None
AlwaysBreakAfterReturnType: None
AlwaysBreakBeforeMultilineStrings: false
AlwaysBreakTemplateDeclarations: false
BinPackArguments: true
BinPackParameters: true
  AfterClass:      true
  AfterControlStatement: true
  AfterEnum:       true
  AfterFunction:   true
  AfterNamespace:  true
  AfterObjCDeclaration: true
  AfterStruct:     true
  AfterUnion:      false
  BeforeCatch:     true
  BeforeElse:      true
  IndentBraces:    false
BreakBeforeBinaryOperators: None
BreakBeforeBraces: Allman
BreakBeforeTernaryOperators: true
BreakConstructorInitializersBeforeComma: false
ColumnLimit: 0
CommentPragmas: '^ IWYU pragma:'
ConstructorInitializerAllOnOneLineOrOnePerLine: false
ConstructorInitializerIndentWidth: 0
ContinuationIndentWidth: 4
Cpp11BracedListStyle: true
DerivePointerAlignment: false
DisableFormat: false
ExperimentalAutoDetectBinPacking: false
ForEachMacros: [ foreach, Q_FOREACH, BOOST_FOREACH ]
IndentCaseLabels: true
IndentWidth: 4
IndentWrappedFunctionNames: false
KeepEmptyLinesAtTheStartOfBlocks: true
MacroBlockBegin: ''
MacroBlockEnd: ''
MaxEmptyLinesToKeep: 2
NamespaceIndentation: None
PenaltyBreakBeforeFirstCallParameter: 100
PenaltyBreakComment: 300
PenaltyBreakFirstLessLess: 120
PenaltyBreakString: 1000
PenaltyExcessCharacter: 10000
PointerAlignment: Left
ReflowComments: true
SortIncludes: false
SpaceAfterCStyleCast: false
SpaceBeforeAssignmentOperators: true
SpaceBeforeParens: ControlStatements
SpaceInEmptyParentheses: false
SpacesBeforeTrailingComments: 1
SpacesInAngles: true
SpacesInContainerLiterals: true
SpacesInCStyleCastParentheses: true
SpacesInParentheses: true
SpacesInSquareBrackets: true
Standard: Cpp11
TabWidth: 4
UseTab: Never

It took me a few hours of fiddling with the settings to find the best combination. It would be really useful if someone could write a tool that would analyze your C++ code and create a .clang-format file for you. You would probably only want to do this once though, so I don’t think it has much potential as a commercial product.

There are only two things I couldn’t get quite right in the formatting:

  1. I couldn’t get it to add a blank line after public, protected and private declarations. I fixed this with a quick Perl hack (see below).
  2. I couldn’t get it to indent continuation lines how I would like (ideally indented 1 or 2 spaces from the first line). It is a small price to pay and I am just putting up with it for now.

Perhaps there are options to do these and I just didn’t find them.

Here is the Windows .bat script I used to format all the C++ files in a folder.

for %%f in (*.h *.cpp *.inl) do (
clang-format.exe -i -style=file %%f

for %%f in (*.h) do (
clang-format.exe -i -style=file %%f
perl -p -i.bak -e "s/public:/public:\n/g" %%f
perl -p -i.bak -e "s/protected:/protected:\n/g" %%f
perl -p -i.bak -e "s/private:/private:\n/g" %%f
perl -p -i.bak -e "s/    Q_OBJECT/Q_OBJECT/g" %%f

del *.bak
del *.tmp

No doubt there is a more elegant way to do the Perl, but it works.

I now just run this batch periodically to keep my code beautiful and consistent.

A code pretty printer product idea

I use QtCreator for my C++ development IDE. It is very good. But it doesn’t always lay out my C++ code the way I want it to. In particular the refactoring operations mess up my white space. I want my code to look like:

void foo( int* x, int& y )

But it keeps changing it to:

void foo(int *x, int &y)


So I am constantly battling with QtCreator to layout my code how I like it. There are plenty of C++ pretty printers around. I played with some of the leading ones using UniversalIndentGUI, but I couldn’t get any of them to layout my code quite how I wanted. Maybe they could have done it, but I got fed up with fiddling with the settings.

What I need is a code pretty printer that I can configure to layout my code exactly how I want without me having to tweak 100 settings.

Ideally I want a code pretty printer that I can train. So I just point it at a few files of my code that are laid out how I want and it works out all my preferences (where to put braces, how to indent case statements, where to put the * for a pointer declaration etc) and can then apply them to any other code. It wouldn’t need a GUI. Or perhaps just enough to select the training files and then preview the results on other files.

I have no idea if this is a viable product idea. But I would pay $100 for it, if it worked well. Perhaps bigger software companies would pay a lot more? Or maybe something like this already exists and I just don’t know about it?

Cppcheck – A free static analyser for C and C++

I got a tip from Anna-Jayne Metcalfe of C++ and QA specialists Riverblade to check out Cppcheck, a free static analyser for C and C++. I ran >100 kLOC of PerfectTablePlan C++ through it and it picked up a few issues, including:

  • variables uninitialised in constructors
  • classes passed by value, rather than as a const reference
  • variables whose scopes could be reduced
  • methods that could be made const

It only took me a few minutes from downloading to getting results. And the results are a lot less noisy than lint. I’m impressed. PerfectTablePlan is heavily tested and I don’t think any of the issues found are the cause of bugs in PerfectTablePlan, but it shows the potential of the tool.

The documentation is here. But, on Windows, you just need to start the Cppcheck GUI (in C:\Program files\Cppcheck, they appear to be too modest to add a shortcut to your desktop), select Check>Directory… and browse to the source directory you want to check. Any issues found will then be displayed.

You can also set an editor to integrate with, in Edit>Preferences>Applications. Double clicking on an issue will then display the appropriate line in your editor of choice.

Cppdepend is available with a GUI on Windows and as a command line tool on a range of platforms. There is also an Eclipse plugin. See the sourceforge page for details on platforms and IDEs supported. You can even write your own Cppcheck rules.

Cppcheck could be a very valuable additional layer in my defence in depth approach to QA. I have added it to my checklist of things to do before each new release.

Programming skills wanted

I am looking to outsource some self-contained programming tasks in areas that I don’t have expertise in. I am hoping that someone reading this blog might be able to help (or know someone that can) so I don’t have to go through outsourcing sites. These are the two skills sets I am currently looking for:

  1. Javascript/CSS/HTML – To write a single page web app. This will have a relatively simple UI displaying data read from XML. The app will need to work on a wide range of browsers and devices. Ideally you should also have some web design skills, but this isn’t essential.
  2. C++/Qt 4/OpenGL – To write a relatively simple 3D visualization model that runs on Windows and Mac. This will involve populating a 3D space with specified shapes and allowing simple movement around it.


  • I am expecting that I will need 2 different people, but it is possible there might be someone out there with experience in both.
  • These are small projects (probably less than 2 weeks for task 1 and less than 1 week for task 2). But they might lead on to more work in future.
  • Time scales are reasonably relaxed. Ideally I would like the work to be finished by the end of September.
  • You can be based anywhere in the world, but must be able to communicate in English (written and spoken).
  • Full copyright to the work will pass to my company on full payment.
  • Obviously cost is an issue. If I have 2 promising candidates, I am likely to pick the cheaper one.

If you are interested in doing either of these tasks please email me ( andy at oryxdigital.com ) before the end of Friday 26th August with subject “programming work” and a brief outline of:

  • Which of the 2 tasks you are interested in.
  • Your relevant experience. Ideally including details of related projects completed.
  • Your daily rate in Pounds Sterlings or US dollars.

I will send detailed specs to a shortlist of the best candidates. The work will be awarded on the basis of fixed price bids against the spec. Please don’t apply unless you have relevant experience – if I wanted a programmer without experience in these areas I could do it myself. ;0)

Presents for programmers

It is coming up to that time of year again. You had better start dropping some hints on what you want for Christmas if you don’t want socks again. How about a software themed T-shirt? You can never have too many T-shirts and it means you can go an extra day before you have to do the laundry.

It just so happens that www.programmer-tshirts.com (set up by myself and Patrick McKenzie last year) carries a range of wittily(?) captioned T-shirts for software types of all stripes including: microISVS, C++ programmers, LISP programmers, Mac developers, software engineers, managers and bloggers. Following on from a conversation at ESWC 2009 (with someone who might prefer to remain anonymous) I have just added another design for server programmers:

I know the T-shirts aren’t cheap (print-on-demand is expensive), but I have ordered a couple myself from the European shop and the quality is very good. Also you can customise the t-shirts (e.g. choose a different colour). Best of all the commission on each T-shirt (12.5% for the US shop and £1.50 for the European shop) goes to two very worthy charities:

  • Sightsavers International works to alleviate sight problems around the world. Every year Sightsavers and their partners treat millions of people for potentially blinding conditions. It costs as little as $0.10 to protect someone from river blindness for a year.
  • Jaipur Foot have developed an effective and easy-to-fit prosthetic lower limb that can be produced for a little as $30. The charity has distributed over 300,000 limbs free of charge in 22 countries.

It won’t be a surprise to regular readers that I am going to finish this post with a less than subtle call-to-action.

(STOP PRESS: 15% off everything in the European shop until 29-Nov-2009, use voucher code: NOVEMBERSALE)

Using a Mac mini for development

mac miniI have been using a Mac mini to port my C++/Qt based code to Mac OS X for the last 3.5 years. This is one of the early PowerPC based Mac minis, upgraded to 1GB of RAM. Being Apple hardware, it is expensive for what you get. But it has served me well. The small form factor (approx 17 x 17 x 5 cm) has also been useful in my cramped office, where I have it attached to the same monitor, mouse and keyboard as my Windows box through a KVM switch. But it is struggling to keep up with PerfectTablePlan’s ever increasing code base. A clean build of the PerfectTablePlan source into a Universal (fat) binary now takes an eye-watering 36 minutes to compile and link on the Mac mini. Building a PowerPC-only debug version still takes nearly half that time. That is painful, even just for occasional porting work.

As my main development environment is Windows, I can’t really justify the cost (or office space requirements) of a Mac Pro. So I decided to buy a new Mac mini, with an Intel Core 2 Duo processor. I did look around to see if I could find one at a discount. However, this being Apple hardware, no-one dares sell  at anything significantly less than Apple’s RRP. I bought the smaller (120GB) disk variant and had the dealer upgrade it to 2GB RAM, which tests on my old Mac mini indicated should be plenty for compiling and linking. I didn’t want to do the memory upgrade myself as I know, from experience with my first Mac mini, that removing the case involves putty knives and some very worrying cracking noises.

I had all sorts of problems trying to get the right cables. Firstly I wanted a Firewire cable so I could copy the set-up across from the old machine to the new machine using Apple’s Migration Assistant software. But it turns out that the old Mac Mini has a Firewire 400 6-pin socket, whereas the new Mac Mini has a Firewire 800 9-pin socket. I ordered a 6-pin to 9-pin Firewire cable cable. Then I discovered that there is more than one type of DVI cable. The old Mac mini was attached to my KVM switch with a DVI-I cable. The new Mac mini only accepts mini-DVI or (via a supplied adaptor) DVI-D. So I ordered a dual link DVI-D to DVI-D cable as well.

Once I had the right cables things went relatively smoothly. The Migration Assistant software copied almost all the apps and data across from the old machine to the new one. It even preserved settings for the apps, e.g. the email accounts in my Thunderbird email client. I just had to re-install XCode (which wasn’t copied across) and rebuild my Qt libraries (to avoid copious warnings due to the fact they had been built with an earlier version of XCode/gcc).

To use the migration assistant you simply:

  1. connect the 2 machines with a Firewire cable
  2. start-up the old machine with the ‘T’ key depresses to put it in ‘Target’ mode
  3. start-up the new machine
  4. follow the on-screen instructions

Nice. If only it was was that easy to set-up a new Windows machine.

A quick test shows that the new Mac mini is nearly 6 times faster at compiling and linking a Universal binary of PerfectTablePlan from scratch[1]:

mac mini performance

The time the new Mac mini takes to compile and link an Intel-only debug release of PerfectTablePlan also compares favourably with a similar build on my Windows 2.13 GHz Intel Core 2 Duo box with 4GB of RAM[2].

mac mini performance 2

This isn’t a fair hardware comparison, as the two machines are using completely different compilers and linkers and the Windows box was running various background services. But it certainly shows that Intel-based Mac minis are worth considering for use as development machines.

[1] The newer machine is using a newer version of XCode/gcc.

[2] The Windows box is using Visual Studio 2005.

C++ for the next decade


Although some people regard C++ as the COBOL of the 21st century, it remains a force to be reckoned with in commercial development. For example it is currently ranked fourth in the language related tags on stackoverflow.com (despite the apparent biases of Stackoverflow owners Jeff Atwood and Joel Spolsky towards web and .Net oriented languages):

Rank Language Tagged questions
1 C# 4681
2 Java 2903
3 ASP.Net 2334
4 C++ 2040
5 Javascript 1677
6 PHP 1505
7 Python 1397
8 C 851
9 Ruby 719
10 VB.Net 548

C++ has been one of the top commercial languages for a long time. But the world of computer software and hardware is changing fast and languages have to evolve to stay relevant. The first major revision to the C++ standard in a decade, known as C++ 0x, is expected be finalised in 2009 (otherwise the x will have to be hex). The draft standard includes lots of additions to the language and standard libraries, including: lambdas; closures; static (compile time) asserts; concepts; automatic types; variadic templates; a regular expressions library and improved threading support. Automatic garbage collection is notable by its absence.

For working C++ developers the new standard only really becomes important when it becomes available in mainstream compilers such as Visual C++ and Gnu C++. As Gnu C++ already has experimental support for C++ 0x and Microsoft released a preview of Visual Studio 2010 at PDC last month with support for some of new features it might be a good time to start paying attention to the new standard. You don’t want to look like an idiot next time one your colleagues starts talking about ‘lambdas’, do you?

I illustrate a few of the new features below. I have done this mainly as a way of understanding them better myself, not because I claim any sort of expertise on the new standard.

Lambdas and closures

A ‘lambda’ is an unnamed function, for example:

std::vector<int> values = getValues();
std::for_each( values.begin(), values.end(), [](int n) { cout << n << std::endl; } );

Lambdas can reference in-scope variables, for example:

std::vector<int> values = getValues();
int total = 0;
std::for_each( values.begin(), values.end(), [&total](int n) { total += n } );

This is known as a ‘closure’. Of course, all of this can be done with standard function calls, but lambdas are undoubtedly more compact and elegant. I am not convinced that they will make code any clearer or easier to debug or maintain however.

Automatic types

Automatic typing allows the compiler to infer a type. For example:

std::vector<int> values = getValues();
for ( std::vector<int>::const_iterator it = values.begin(); it != values.end(); ++it ) { f( it ); }

Can be re-written as:

auto values = getValues();
for ( auto it = values.begin(); it != values.end(); ++it ) { f( it ); }

Automatic types seem like an excellent way to let the compiler take some of the drudgery out of programming.


Template error messages have improved over the years, but they can still be obscure. A ‘concept’ is a way to clearly define what types a templated class or function will accept. For example:

template<typename T> requires LessThanComparable<T>
const T& min(const T &x, const T &y)
return y < x ? y : x;

Specifies that min() will only accept types that support the concept LessThanComparable.  LessThanComparable can then be defined so that the type must support the < operator:

auto concept LessThanComparable<typename T>
bool operator<(T, T);

Hopefully concepts will allow better defined template interfaces and clearer error messages.


The current C++ standard makes no real allowances for concurrency. This is a major problem in a world where multi-core CPUs are standard. The new standard will introduce a memory model that supports threading and a standard threading library.


C++ has many strengths. It scores quite highly on performance, expressiveness and portability, has an extensive tool and library ‘ecosystem’ and a proven track record in large scale system development. But it is also a sprawling and complex language, hobbled by many shortcomings inherited from its progenitor C (a language dating back to the early seventies). It isn’t clear to me whether the new standard will add enough features to keep C++ competitive as a commercial language for another decade. Or whether C++ will be regarded as a legacy language, too bloated and complex to attract new developers given the choice of simpler and more elegant languages. Time will tell.

Further reading:

C++ 0x article on wikipedia