January 2014 - Boost - lists.preview.boost.org

sqlpp11: SQL for C++
by Roland Bock 06 Feb '14

06 Feb '14

Hi, over the last four or five years I developed several SQL libraries for C++. With C++11 I was finally able to create an SQL library that meets my own expectations and requirements. It is being used in production, I recently put it on github, and I would really like to hear from you guys whether this is something that could be interesting for you personally or for boost? https://github.com/rbock/sqlpp11 https://github.com/rbock/sqlpp11/wiki sqlpp11 is a template library representing an embedded domain specific language (EDSL) that allows you to * define types representing tables and columns, * construct type safe queries checked at compile time for syntax errors, type errors, name errors and even some semantic errors, * interpret results by iterating over query-specific structs with appropriately named and typed members. This results in several benefits, e.g. * the library user operates comfortably on structs and functions, * the compiler reports many kinds of errors long before the code enters unit testing or production, * the library hides the gory details of string construction for queries and interpreting string based results returned by select calls. I.e. you don't need to use strings in query construction where you wouldn't use them in SQL and there is no need to use positional arguments or to parse strings when obtaining fields from a result row (the latter being true unless you do not know which columns to select at compile time). The library supports both static and dynamic queries. The former offers greater benefit in terms of type and consistency checking. The latter makes it easier to construct queries on the flight. Specific traits of databases (e.g. unsupported or non-standard features) are known at compile time as well. This way, the compiler can tell the developer at compile time if a query is not accepted by the database (e.g. if a feature is missing). And the library can form the query in the correct manner, for instance if the engine uses concat instead of operator|| to concatenate strings. Two Examples: ============= Static Select: -------------- // selecting zero or more results, iterating over the results for (const auto& row : db.run( select(foo.name, foo.hasFun) .from(foo) .where(foo.id > 17 and foo.name.like("%bar%")))) { if (row.name.is_null()) std::cerr << "name will convert to empty string" << std::endl; std::string name = row.name; // text fields are implicitly convertible to string bool hasFun = hasFun; // bool fields are implicitly convertible to bool } Dynamic Select: ---------------- auto s = dynamic_select(db, tab.foo).dynamic_columns().from(tab); if (userWantsBar) s.add_column(tab.bar); for(const auto& row : run(s)) { std::cerr << "row.foo: " << row.foo; if (userWantsBar) std::cerr << "row.bar" << row.at("bar"); std::cerr << std::endl; }; Please let me know your questions/thoughts/suggestions/rants. Contributions welcome, of course :-) Regards, Roland

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Trying modular Boost
by Paul A. Bristow 04 Feb '14

04 Feb '14

FWIW here are some things I didn't understand or did wrong. (And, of course, playing Devil's Decidedly Dumb Advocate ;-) 1 How do I know if I have the right version of Git? Open GitHub icon and check Tools/About? 2 Windows hint: If you install TortoiseGIT, avoid incompatibilities by using the command line version of Git that TortoiseGIT installs. I.E. place C:\Program Files (x86)\Git\cmd in your path ahead of any other git binaries, such as cygwin. Huh? Am I Shelling, Bashing, Batting or Powershelling? How do I do that? How do I check that I have done this right? Open a Windows command window? Many Windowers will not know how to find/edit their path (and should not need to know?). A link would help. If you have dozens of items in the path, this is pretty awkward to edit? But (after a frustrating failure to get SSH access to work - in a separate post) I got to the main course using https: https://github.com/boostorg/boost.git Submodule 'io' (https://github.com/boostorg/io.git) registered for path 'libs/io' Submodule 'iostreams' (https://github.com/boostorg/iostreams.git) registered for path 'libs/iostreams' <big snip> Cloning into 'tools/quickbook'... Submodule path 'tools/quickbook': checked out '340c65150d175ffc20a9a877247928b3ed5eba1b' Success (4040769 ms @ 31-Dec-2013 17:00:21) Just over an hour (using my nominal 10 mbps living-in-the-boondocks but line-of-sight radio link) - something that should be noted in the docs (along with a strong recommendation to send to a log file)? Other you would miss/lose this very useful info? Building the Boost C++ Libraries. Performing configuration checks - symlinks supported : no - hardlinks supported : yes - 32-bit : yes . And I could test system library OK J Phew! Paul PS I had an existing (luckily current) b2.exe at c:\program files\Boost and this is implicitly in my PATH. Do we need to be more specific about how b2 is stored and accessed? Some check that b2.exe vcvars32.bat etc are all set up correctly would be good? --- Paul A. Bristow, Prizet Farmhouse, Kendal LA8 8AB UK +44 1539 561830 07714330204 <mailto:pbristow@hetp.u-net.com> pbristow(a)hetp.u-net.com

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Process for the Community Maintenance Team
by Marshall Clow 04 Feb '14

04 Feb '14

I’ve put up a set of procedures for the Boost Community Maintenance Team (CMT) on the wiki at: https://svn.boost.org/trac/boost/wiki/CommunityMaintenance Comments welcomed. — Marshall

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named_condition_any not working.
by Marius Adrian DOBRESCU 02 Feb '14

02 Feb '14

Hello! I tried to use into my code an interprocess mechanism like producer/multiple consumers with named_sharable_mutexes. I found out that named_condition_any is not working with any kind of scoped locks. Neither with sharable_mutex or simple named_mutex. It takes the lock successful but cannot unblock another process when notify is called. I used linux, gcc 4.8, just basic build, linking with pthreads. Is this a known issue to you because I couldn't find any info related on the Internet? Maybe I can take a look next week what is in there... Adrian

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[offtopic] user-defined raw string literals
by Adam Wulkiewicz 01 Feb '14

01 Feb '14

Hi, I have some idea related to the usage of UDLs in Boost.Geometry library but the way I'd like to handle it is AFAIK not supported. A little introduction first. There are many text-based languages of defining data. One of them is WKT (http://en.wikipedia.org/wiki/Well-known_text) which allows to define vector data e.g. a polygon like this: |POLYGON((30 10, 40 40, 20 40, 10 20, 30 10))| So my thought was: why not use C++11 UDLs for this purpose? There are operators in the WKT language so I should probably use string literal, put WKT in it and be happy with it. The use case could look like this: |auto ||polygon = "POLYGON((30 10,40 40,20 40,10 20,30 10))|"_wkt; Ok so now the tricky part. It should be parsed in compile-time, the type of the geometry retrieved from the string literal and proper type returned (bg::polygon<> in this case). Unfortunately string literals can't be handled as raw literals, e.g. using the variadic-template version of operator"": template <char...> void operator "" () Why? Is there a reason for this? If we had the ability to use the compile-time version with string literals it would be possible to implement various compile-time parsers, not only for the mentioned WKT. So what do you think about it? Regards, Adam

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[docs][website] Can the docs on the website be xhtml + svg?
by John Maddock 01 Feb '14

01 Feb '14

I've been investigating getting better equations and graphs into the Math lib docs and one prerequisite seems to be serving up pages as XHTML rather than HTML: without that SVG's simply do not display correctly (or at all) in IE. The docbook xhtml generation seems to be working OK, but would the pages get served correctly on the current website? Thanks, John.

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[conversion] Need a help with MSVC failures
by Antony Polukhin 01 Feb '14

01 Feb '14

Hi, Some of the tests for Boost.LexicalCast fail on any MSVC compiler. Unfortunately currently I have no access to Windows. Could someone please investigate the failures and tell me were to search the bug? -- Best regards, Antony Polukhin

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[range] Can iterator_range also model Random Access Range?
by Mostafa 01 Feb '14

01 Feb '14

It seems that iterator_range can properly model any refinement of the Forward Range concept. Is that right? The reason I ask is that this is not very clear from the documentation, and I had to deduce this from both the iterator_range API and the Random Access Range concept definition. (See documentation at: range/reference/utilities/iterator_range.html) Thanks, Mostafa

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Range Adapters (map_keys, map_values) cause undefined behavior (segv, etc) when applied to R-Values, especially in the context of BOOST_FOREACH
by Igor Lubashev 01 Feb '14

01 Feb '14

Hi! I've filed a ticket (https://svn.boost.org/trac/boost/ticket/9578) for this issue two weeks ago, but I see no action there. Does anyone else think that this (see subj) is a problem? To spare the trouble of following the link, here is the essence of the problem, as I see it. (The ticket has a simple test case attached.) When applied to r-values (for example, maps returned by value from a function), adapters do not make a copy of the r-value but just capture a reference to it. This makes the returned range_iterator dangerous, if it is used after the r-value (the temporary) is destroyed. In particular, the following use causes undefined behavior on all compilers I'd tested on: g++ (4.1.2, 4.4.3, 4.6.3) and Visual Studio (15 [VC9], 16 [VC10]). BOOST_FOREACH(const string &s, return_map_by_value() | map_keys) ... Note that the following works fine (since BOOST_FOREACH takes care of differentiating between l-values and r-values and does the right thing to r-values): BOOST_FOREACH(const MapType::value_type &v, return_map_by_value()) ... It seems that boost::range::adapters need to do a similar thing to what BOOST_FOREACH is does to identify r-values and make a copy (which the compiler is likely to optimize away). Any comments are welcome! Thanks, - Igor

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Re: [boost] Participation in GSOC 2014
by Vineet Kumar, Indian Institute of Technology, BHU, Varanasi (INDIA) 31 Jan '14

31 Jan '14

Hello Everyone, I want to participate in GSOC 2014, and boost C++ is looking me the most appropriate place where I can contribute efficiently. So how to get started with boost C++ libraries ? I have an Idea of implementing a library in boost. So what I do then , concentrate on library or something else With Regards Vineet Kumar, Indian Institute of Technology, BHU

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