August 2008 - Boost - lists.boost.org

[PATCH: MPL] Compiling with gcc 4.4.0 -std=c++0x
by Chris Fairles 21 Aug '08

21 Aug '08

Due to pre-processor changes in gcc 4.4.0, MPL fails to compile given -std=c++0x or -std=gnu++0x on the command line. The attached patch addresses this issue. This is a works-for-me solution, YMMV. Chris

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Where does make_shared.hpp come from?
by Boris 20 Aug '08

20 Aug '08

I stumbled over boost::make_shared() in Andrey's logging library. I checked the smart pointers documentation at http://www.boost.org/doc/libs/1_36_0/libs/smart_ptr/smart_ptr.htm but couldn't find any reference to boost::make_shared(). The header file make_shared.hpp contains the link http://www.boost.org/libs/smart_ptr/make_shared.html but the webpage doesn't exist either. Is boost::make_shared() not yet documented? Boris

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[log] Questions for Andrey
by Boris 20 Aug '08

20 Aug '08

I've been converting a program from John's logging library to Andrey's logging library. I have to continue playing around with Andrey's library but in the moment I prefer it over John's library. I can't say really that this or that is better - it's more the overall handling of Andrey's logging library which feels more natural for me. Maybe it's also Andrey's documentation which is rather good (the definitions and design overview really help to understand the big picture before you dive into all the details). I've some questions though for Andrey: * Where is the connection between a source and a sink? In the basic_usage example there are two sinks registered (console and file). There is then one source created which is used to log a message. The message is then sent to both the console and the file. But what if I want to use for example two sources and want messages from each source to be sent to a different sink? Do I understand correctly that I need to use attributes somehow and filter records based on attribute values? I guess I would need to add an attribute to each source and set a filter in each sink to make sure only messages with a certain attribute are written? * If I want to format a message and add a timestamp why do I need to write boost::log::formatters::date_time("TimeStamp") and can't write boost::log::formatters::attr("TimeStamp")? Doesn't the attribute value know how to be serialized (or isn't it written to a std::ostream)? If I use boost::log::formatters::attr("TimeStamp") nothing is written to the log file. It's not a problem to use boost::log::formatters::date_time("TimeStamp") of course. But I still wonder why the library can't figure out to write the timestamp if I use boost::log::formatters::attr("TimeStamp"). * I've been reading http://boost-log.sourceforge.net/libs/log/doc/html/advanced/advanced.html#a… a few times but still don't understand why I can't (or shouldn't) instantiate a global logger with "boost::log::sources::logger logger;". I actually did this and everything works (or at least seems to work :). Must the macro BOOST_LOG_DECLARE_GLOBAL_LOGGER really be used when a global logger is created? Maybe I better understand if I ask differently: What is so special about a logger that I need to use a macro to define it globally while I can create for example a global std::string instance without a macro? * By default there is a newline appended to every message written? By the way, looking at the TODO list: I would be very much interested in Windows NT event log support. I'm sure it would also convince more developers to use a logging library as writing texts to files in some fancy ways can also be done without a logging library. :) Boris

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[log] More questions for Andrey (how to add function signature to messages)
by Boris 20 Aug '08

20 Aug '08

Currently I'm writing messages to a file with: BOOST_LOG(mylogger) << __FUNCSIG__ << " message text"; I'd prefer if the function signature (let's assume for now that the macro is supported by all compilers) is written automatically without me having to add __FUNCSIG__ everywhere. From what I understand I can't simply add an attribute to the logger as __FUNCSIG__ would then be used in another function (and thus a different function signature would be written). Looking around in the documentation I found BOOST_LOG_WITH_PARAMS (see http://boost-log.sourceforge.net/libs/log/doc/html/BOOST_LOG_WITH_PARAMS.ht…) It makes me think that I could define my own BOOST_LOG macro somehow like this: #define BOOST_LOG_FUNCSIG(logger)\ BOOST_LOG_WITH_PARAMS((logger), (::boost::log::sources::keywords::funcsignature = (__FUNCSIG__))) I see that the macro BOOST_LOG_SEV is defined similarly in severity_logger.hpp. However I also see that some more code has to be added to the logger to make the logger understand what to do with the keyword. For example in the severity logger in open_record() the appropriate attribute is set if the severity keyword is found. That means I would need to create a new logger and check for my new funcsignature attribute in open_record() if I want the function signature to be written automatically? Is there another way to do this more easily? Boris

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[exception] missing workarounds for msvc 4265 warning
by Jürgen Hunold 20 Aug '08

20 Aug '08

Hi ! My coworkers found some more annoying msv 4265 warnings. (missing virtual destructor. The attached patch adds the necessary workaround (analog to gcc). Okay to commit ? Yours, Jürgen -- * Dipl.-Math. Jürgen Hunold ! Ingenieurgesellschaft für * voice: ++49 511 262926 57 ! Verkehrs- und Eisenbahnwesen mbH * fax : ++49 511 262926 99 ! Lister Straße 15 * juergen.hunold(a)ivembh.de ! www.ivembh.de * * Geschäftsführer: ! Sitz des Unternehmens: Hannover * Prof. Dr.-Ing. Thomas Siefer ! Amtsgericht Hannover, HRB 56965 * PD Dr.-Ing. Alfons Radtke !

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[config] disabling hash_map/set by #define BOOST_NO_HASH
by Juergen Hunold 20 Aug '08

20 Aug '08

Hi ! After upgrading to gcc-4.3 I got annoyed by the myriads of deprecated warnings about "hash_map" and "hash_set" especially from the BGL code. I tried to get rid of those by simply adding #define BOOST_NO_HASH to the command line and it worked. Unfortunately, it seems that trunk config does not detect hash support with msvc-8.0 and this compiler then bailed out with a macro redefinition error at config/suffix.hpp :-(( Patch to add a check for an already defined BOOST_NO_HASH (and for BOOST_NO_SLIST) attached. Comments ? Ok to commit ? Better ideas to disable hash support ? Yours, Jürgen -- * Dipl.-Math. Jürgen Hunold ! Ingenieurgesellschaft für * voice: ++49 511 262926 57 ! Verkehrs- und Eisenbahnwesen mbH * fax : ++49 511 262926 99 ! Lister Straße 15 * juergen.hunold(a)ivembh.de ! www.ivembh.de * * Geschäftsführer: ! Sitz des Unternehmens: Hannover * Prof. Dr.-Ing. Thomas Siefer ! Amtsgericht Hannover, HRB 56965 * PD Dr.-Ing. Alfons Radtke !

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[integer] Recent changes introduced failures on many platforms
by Markus Schöpflin 20 Aug '08

20 Aug '08

The two tests integer_mask_test and integer_test have been broken by the recent commits to integer on nearly all platforms. (Probably all but Windows) The error message is: In file included from ../libs/integer/test/integer_test.cpp:29: ../boost/integer.hpp:154:39: error: invalid suffix "ui64" on integer constant ../libs/integer/test/integer_test.cpp:115:39: error: invalid suffix "ui64" on integer constant ../libs/integer/test/integer_test.cpp:215:39: error: invalid suffix "ui64" on integer constant Regards, Markus

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[fsm review] Comparison with ad-hoc FSM coding
by Phil Endecott 20 Aug '08

20 Aug '08

Dear All, I have just spent a few minutes comparing an ad-hoc FSM implementation with an implementation using the proposed library. The example that I've used is the USB device state machine, which I recently had to understand for an embedded application, and I've put an image of the state graph here: http://chezphil.org/tmp/fsm.png For more info, google("USB 2.0 spec") (you'll find a zip file with a PDF in it) and see the start of chapter 9. Note that it seems to me that the "power interruption" transition is wrong and should go to "attached" rather than "powered", and that I have ignored the "suspended" states. The behaviour is essentially as follows: a device is "attached" until the hub supplies power, when it becomes "powered". It then waits for a reset, at which point it starts listening for messages at the "default address" (zero); the host ensures that only one device is in this state at any time. When the host sends a set_address message it changes to the "address" state, and when the host sends a set_configuration message it changes to the "configured" state for normal operation. Here is my ad-hoc implementation (note that I haven't tried to even compile any of this code): struct usb_device { enum state_t { Attached, Powered, Default, Address, Configured }; state_t state; int addr; int configuration; usb_device(): state(Attached), addr(0), configuration(0) {} void power_on() { state = Powered; } void power_off() { state = Attached; } void reset() { state = Default; addr = 0; configuration = 0; } void set_address(int addr_) { addr = addr_; state = (addr==0) ? Default : Configured; } void set_configuration(int configuration_) { configuration = configuration_; state = (configuration==0) ? Address : Configured; } }; In comparison, here's what I've come up with using Boost.FSM: struct Attached; struct Powered; struct Default; struct Address; struct Configured; typedef mpl::vector<Attached, Powered, Default, Address, Configured>::type StateList; struct PowerOn; struct PowerOff; struct Reset; struct SetAddress { int addr; SetAddress(int addr_): addr(addr_) {} }; struct SetConfiguration { int configuration; SetConfiguration(int configuration_): configuration(configuration_) {} }; struct Common { int addr; int configuration; }; struct Attached: fsm::state<Attached,StateList>, Common { void on_process(const PowerOn&) { switch_to<Powered>(); } }; struct Powered: fsm::state<Powered,StateList>, Common { void on_process(const PowerOff&) { switch_to<Attached>(); } void on_process(const Reset&) { switch_to<Default>(); } }; struct Default: fsm::state<Default,StateList>, Common { void on_enter_state() { addr = 0; } void on_process(const PowerOff&) { switch_to<Attached>(); } void on_process(const Reset&) { } void on_process(const SetAddress& set_address) { addr = set_address.addr; if (addr != 0) { switch_to<Address>(); } } }; struct Address: fsm::state<Address,StateList>, Common { void on_process(const PowerOff&) { switch_to<Attached>(); } void on_process(const Reset&) { switch_to<Default>(); } void on_process(const SetAddress& set_address) { addr = set_address.addr; if (addr == 0) { switch_to<Default>(); } } void on_process(const SetConfiguration& set_configuration) { configuration = set_configuration.configuration; if (configuration != 0) { switch_to<Configured>(); } } }; struct Configured: fsm::state<Configured,StateList>, Common { void on_process(const PowerOff&) { switch_to<Attached>(); } void on_process(const Reset&) { switch_to<Default>(); } void on_process(const SetConfiguration& set_configuration) { configuration = set_configuration.configuration; if (configuration == 0) { switch_to<Address>(); } } }; The latter is clearly more verbose than the former. Some of the verbosity would go if I put the common events (e.g. PowerOff) into a base class, but that adds verbosity of its own. There are a few characteristics of this particular design that favour the ad-hoc code. Firstly, the device's behaviour is allowed to be undefined if an unexpected event occurs. Secondly, many events have the same effect irrespective of the state (e.g. power off). Finally, the effect of events often depends on their data (i.e. zero has a special meaning). I would also say that the turnstile example given in the library documentation could be implemented more concisely using an ad-hoc approach (would someone like to try?). Perhaps more complex FSMs would benefit more from what this library offers. In that case, can we see an example? I note that this library is targeted at simpler FSMs than Boost.Statechart (which I have not used). Is there a category of FSMs that are simple enough that Boost.Statechart's features are not needed (e.g. hierarchy) yet too complex for an ad-hoc implementation? Regards, Phil.

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[asio] Resolving Aliases
by Dean Michael Berris 20 Aug '08

20 Aug '08

Hi Guys, While writing the HTTP client in the C++ Networking Library, I ran into a bizarre problem: resolving virtual hosts. For example, given a host named 'bucket.s3.amazonaws.com', trying to resolve it with Boost.Asio (in 1.35) causes a 'Host not found (authoritative)' error. Is this a known issue, and if so what's my alternative? TIA -- Dean Michael C. Berris Software Engineer, Friendster, Inc.

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Need opinion on implementation issue
by Daryle Walker 20 Aug '08

20 Aug '08

I have a class that has the cool pubic member access without "()", like "left" and "right" for boost::bimap. In my case, it's meant to simulate a function object, so it can be passed to functions like std::for_each, and the return value from said functions (the updated function object) can be assigned back to the special member. This function object forwards to the actual computation object within my class object. I implemented this by making a special inner private class and have the auxiliary function object be a public data member of that private type. The actual computation object isn't directly in my class object, but within the public auxiliary member. So the auxiliary function object can be passed by copy or assignment and everything works. The problem is in a class derived from my first one. It also has a public auxiliary function object data member. However, it forwards to the SAME actual computation object as the base class's auxiliary member. I implemented this by the derived class's auxiliary keeping a pointer to the computation object within the base's auxiliary. The issue is when I create temporary derived-auxiliaries for use in std::for_each. I have to create a copy of the computation object with new and delete on destruction. The derived-auxiliary keeps a bool flag indicating whether the pointer points to a contained object or a heap one. I was thinking of making a boost::variant<CompObj, CompObj*> instead, but trades use of the heap for temporaries for making all derived-auxiliaries huge (if sizeof(CompObj) > sizeof (CompObj*)): Current: base's CompObj + derived's CompObj* and bool New: base's CompObj + derived's variant -> base's CompObj + derived's max(CompObj, CompObj*) -> 2 * CompObj (None of these include the various administrative padding or "otherwise empty" bytes.) I haven't changed it yet because I suspect this is a bad trade-off. But what happens on systems with low/no heaps? Should this be some sort of macro switch? -- Daryle Walker Mac, Internet, and Video Game Junkie darylew AT hotmail DOT com

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