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  • C++ Implicit Conversion Operators

    - by Imbue
    I'm trying to find a nice inheritance solution in C++. I have a Rectangle class and a Square class. The Square class can't publicly inherit from Rectangle, because it cannot completely fulfill the rectangle's requirements. For example, a Rectangle can have it's width and height each set separately, and this of course is impossible with a Square. So, my dilemma. Square obviously will share a lot of code with Rectangle; they are quite similar. For examlpe, if I have a function like: bool IsPointInRectangle(const Rectangle& rect); it should work for a square too. In fact, I have a ton of such functions. So in making my Square class, I figured I would use private inheritance with a publicly accessible Rectangle conversion operator. So my square class looks like: class Square : private Rectangle { public: operator const Rectangle&() const; }; However, when I try to pass a Square to the IsPointInRectangle function, my compiler just complains that "Rectangle is an inaccessible base" in that context. I expect it to notice the Rectangle operator and use that instead. Is what I'm trying to do even possible? If this can't work I'm probably going to refactor part of Rectangle into MutableRectangle class. Thanks.

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  • Are memory leaks ever ok?

    - by Imbue
    Is it ever acceptable to have a memory leak in your C or C++ application? What if you allocate some memory and use it until the very last line of code in your application (for example, a global object's deconstructor)? As long as the memory consumption doesn't grow over time, is it OK to trust the OS to free your memory for you when your application terminates (on Windows, Mac, and Linux)? Would you even consider this a real memory leak if the memory was being used continuously until it was freed by the OS. What if a third party library forced this situation on you? Would refuse to use that third party library no matter how great it otherwise might be? I only see one practical disadvantage, and that is that these benign leaks will show up with memory leak detection tools as false positives.

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  • Using time facets on universal_time

    - by scooterman
    Hi all, on boost, to create a time facet to format an specified time we use the folowing: boost::local_time::local_time_facet* facet = new boost::local_time::local_time_facet("%Y%m%d %H:%M:%S.%f"); std::stringstream date_stream; date_stream.imbue(std::locale(date_stream.getloc(), facet)); date_stream << boost::local_time::local_microsec_clock::local_time(boost::local_time::time_zone_ptr()); How do I do the same thing, but using an universal clock: boost::posix_time::microsec_clock::universal_time() Thanks

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  • overriding ctype<wchar_t>

    - by Potatoswatter
    I'm writing a lambda calculus interpreter for fun and practice. I got iostreams to properly tokenize identifiers by adding a ctype facet which defines punctuation as whitespace: struct token_ctype : ctype<char> { mask t[ table_size ]; token_ctype() : ctype<char>( t ) { for ( size_t tx = 0; tx < table_size; ++ tx ) { t[tx] = isalnum( tx )? alnum : space; } } }; (classic_table() would probably be cleaner but that doesn't work on OS X!) And then swap the facet in when I hit an identifier: locale token_loc( in.getloc(), new token_ctype ); … locale const &oldloc = in.imbue( token_loc ); in.unget() >> token; in.imbue( oldloc ); There seems to be surprisingly little lambda calculus code on the Web. Most of what I've found so far is full of unicode ? characters. So I thought to try adding Unicode support. But ctype<wchar_t> works completely differently from ctype<char>. There is no master table; there are four methods do_is x2, do_scan_is, and do_scan_not. So I did this: struct token_ctype : ctype< wchar_t > { typedef ctype<wchar_t> base; bool do_is( mask m, char_type c ) const { return base::do_is(m,c) || (m&space) && ( base::do_is(punct,c) || c == L'?' ); } const char_type* do_is (const char_type* lo, const char_type* hi, mask* vec) const { base::do_is(lo,hi,vec); for ( mask *vp = vec; lo != hi; ++ vp, ++ lo ) { if ( *vp & punct || *lo == L'?' ) *vp |= space; } return hi; } const char_type *do_scan_is (mask m, const char_type* lo, const char_type* hi) const { if ( m & space ) m |= punct; hi = do_scan_is(m,lo,hi); if ( m & space ) hi = find( lo, hi, L'?' ); return hi; } const char_type *do_scan_not (mask m, const char_type* lo, const char_type* hi) const { if ( m & space ) { m |= punct; while ( * ( lo = base::do_scan_not(m,lo,hi) ) == L'?' && lo != hi ) ++ lo; return lo; } return base::do_scan_not(m,lo,hi); } }; (Apologies for the flat formatting; the preview converted the tabs differently.) The code is WAY less elegant. I does better express the notion that only punctuation is additional whitespace, but that would've been fine in the original had I had classic_table. Is there a simpler way to do this? Do I really need all those overloads? (Testing showed do_scan_not is extraneous here, but I'm thinking more broadly.) Am I abusing facets in the first place? Is the above even correct? Would it be better style to implement less logic?

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  • Simplest way to get current time in current timezone using boost::date_time ?

    - by timday
    If I do date +%H-%M-%S on the commandline (Debian/Lenny), I get a user-friendly (not UTC, not DST-less, the time a normal person has on their wristwatch) time printed. What's the simplest way to obtain the same thing with boost::date_time ? If I do this: std::ostringstream msg; boost::local_time::local_date_time t = boost::local_time::local_sec_clock::local_time( boost::local_time::time_zone_ptr() ); boost::local_time::local_time_facet* lf( new boost::local_time::local_time_facet("%H-%M-%S") ); msg.imbue(std::locale(msg.getloc(),lf)); msg << t; Then msg.str() is an hour earlier than the time I want to see. I'm not sure whether this is because it's showing UTC or local timezone time without a DST correction (I'm in the UK). What's the simplest way to modify the above to yield the DST corrected local timezone time ? I have an idea it involves boost::date_time:: c_local_adjustor but can't figure it out from the examples.

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  • Reading in Russian characters (Unicode) using a basic_ifstream<wchar_t>

    - by Mark
    Is this even possible? I've been trying to read a simple file that contains Russian, and it's clearly not working. I've called file.imbue(loc) (and at this point, loc is correct, Russian_Russia.1251). And buf is of type basic_string<wchar_t> The reason I'm using basic_ifstream<wchar_t> is because this is a template (so technically, basic_ifstream<T>, but in this case, T=wchar_t). This all works perfectly with english characters... while (file >> ch) { if(isalnum(ch, loc)) { buf += ch; } else if(!buf.empty()) { // Do stuff with buf. buf.clear(); } } I don't see why I'm getting garbage when reading Russian characters. (for example, if the file contains ??? ??? ???, I get "??E", 5(square), K(square), etc...

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  • c++ unicode writing is not working

    - by Jugal Kishore
    I am trying to write some Russian unicode text in file by wfstream. Following piece of code has been used for it. wfstream myfile; locale AvailLocale("Russian"); myfile.imbue(AvailLocale); myfile.open(L"d:\\example.txt",ios::out); if (myfile.is_open()) { myfile << L"?????? ????" <<endl; } myfile.flush(); myfile.close(); Something unrecognizable is written to the file by executing this code, I am using VS 2008.

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  • getting boost::gregorian dates from a string

    - by Chris H
    I asked a related question yesterday http://stackoverflow.com/questions/2612343/basic-boost-date-time-input-format-question It worked great for posix_time ptime objects. I'm have trouble adapting it to get Gregorian date objects. try { stringstream ss; ss << dateNode->GetText(); using boost::local_time::local_time_input_facet; //using boost::gregorian; ss.imbue(locale(locale::classic(), new local_time_input_facet("%a, %d %b %Y "))); ss.exceptions(ios::failbit); ss>>dayTime; } catch (...) { cout<<"Failed to get a date..."<<endl; //cout<<e.what()<<endl; throw; } The dateNode-GetText() function returns a pointer to a string of the form Sat, 10 Apr 2010 19:30:00 The problem is I keep getting an exception. So concretely the question is, how do I go from const char * of the given format, to a boost::gregorian::date object? Thanks again.

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  • Who architected / designed C++'s IOStreams, and would it still be considered well-designed by today'

    - by stakx
    First off, it may seem that I'm asking for subjective opinions, but that's not what I'm after. I'd love to hear some well-grounded arguments on this topic. In the hope of getting some insight into how a modern streams / serialization framework ought to be designed, I recently got myself a copy of the book Standard C++ IOStreams and Locales by Angelika Langer and Klaus Kreft. I figured that if IOStreams wasn't well-designed, it wouldn't have made it into the C++ standard library in the first place. After having read various parts of this book, I am starting to have doubts if IOStreams can compare to e.g. the STL from an overall architectural point-of-view. Read e.g. this interview with Alexander Stepanov (the STL's "inventor") to learn about some design decisions that went into the STL. What surprises me in particular: It seems to be unknown who was responsible for IOStreams' overall design (I'd love to read some background information about this — does anyone know good resources?); Once you delve beneath the immediate surface of IOStreams, e.g. if you want to extend IOStreams with your own classes, you get to an interface with fairly cryptic and confusing member function names, e.g. getloc/imbue, uflow/underflow, snextc/sbumpc/sgetc/sgetn, pbase/pptr/epptr (and there's probably even worse examples). This makes it so much harder to understand the overall design and how the single parts co-operate. Even the book I mentioned above doesn't help that much (IMHO). Thus my question: If you had to judge by today's software engineering standards (if there actually is any general agreement on these), would C++'s IOStreams still be considered well-designed? (I wouldn't want to improve my software design skills from something that's generally considered outdated.)

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  • Are C++ exceptions sufficient to implement thread-local storage?

    - by Potatoswatter
    I was commenting on an answer that thread-local storage is nice and recalled another informative discussion about exceptions where I supposed The only special thing about the execution environment within the throw block is that the exception object is referenced by rethrow. Putting two and two together, wouldn't executing an entire thread inside a function-catch-block of its main function imbue it with thread-local storage? It seems to work fine: #include <iostream> #include <pthread.h> using namespace std; struct thlocal { string name; thlocal( string const &n ) : name(n) {} }; thlocal &get_thread() { try { throw; } catch( thlocal &local ) { return local; } } void print_thread() { cerr << get_thread().name << endl; } void *kid( void *local_v ) try { thlocal &local = * static_cast< thlocal * >( local_v ); throw local; } catch( thlocal & ) { print_thread(); return NULL; } int main() try { thlocal local( "main" ); throw local; } catch( thlocal & ) { print_thread(); pthread_t th; thlocal kid_local( "kid" ); pthread_create( &th, NULL, &kid, &kid_local ); pthread_join( th, NULL ); print_thread(); return 0; } Is this novel or well-characterized? Was my initial premise correct? What kind of overhead does get_thread incur in, say, GCC and VC++? It would require throwing only exceptions derived from struct thlocal, but altogether this doesn't feel like an unproductive insomnia-ridden Sunday morning…

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  • C++ simple logging class with UTF-8 output [code example]

    - by Andrew
    Hello everyone, I was working on one of my academic projects and for the first time I needed pure C++ without GUI. After googling for a while, I did not find any simple and easy to use implementation for logging and created my own. This is a simple implementation with iostreams that logs messages to screen and to the file simultaneously. I was thinking of using templates but then I realized that I do not expect any changes and removed that. It is modified std::wostream with two added modifiers: 1. TimeStamp - prints time-stamp 2. LogMode(LogModes) - switches output: file only, screen only, file+screen. *Boost::utf8_codecvt_facet* is used for UTF-8 output. // ############################################################################ // # Name: MyLog.h # // # Purpose: Logging Class Header # // # Author: Andrew Drach # // # Modified by: <somebody> # // # Created: 03/21/10 # // # SVN-ID: $Id$ # // # Copyright: (c) 2010 Andrew Drach # // # Licence: <license> # // ############################################################################ #ifndef INCLUDED_MYLOG_H #define INCLUDED_MYLOG_H // headers -------------------------------------------------------------------- #include <string> #include <iostream> #include <fstream> #include <exception> #include <boost/program_options/detail/utf8_codecvt_facet.hpp> using namespace std; // definitions ---------------------------------------------------------------- // ---------------------------------------------------------------------------- // DblBuf class // Splits up output stream into two // Inspired by http://wordaligned.org/articles/cpp-streambufs // ---------------------------------------------------------------------------- class DblBuf : public wstreambuf { private: // private member declarations DblBuf(); wstreambuf *bf1; wstreambuf *bf2; virtual int_type overflow(int_type ch) { int_type eof = traits_type::eof(); int_type not_eof = !eof; if ( traits_type::eq_int_type(ch,eof) ) return not_eof; else { char_type ch1 = traits_type::to_char_type(ch); int_type r1( bf1on ? bf1->sputc(ch1) : not_eof ); int_type r2( bf2on ? bf2->sputc(ch1) : not_eof ); return (traits_type::eq_int_type(r1,eof) || traits_type::eq_int_type(r2,eof) ) ? eof : ch; } } virtual int sync() { int r1( bf1on ? bf1->pubsync() : NULL ); int r2( bf2on ? bf2->pubsync() : NULL ); return (r1 == 0 && r2 == 0) ? 0 : -1; } public: // public member declarations explicit DblBuf(wstreambuf *bf1, wstreambuf *bf2) : bf1(bf1), bf2(bf2) { if (bf1) bf1on = true; else bf1on = false; if (bf2) bf2on = true; else bf2on = false; } bool bf1on; bool bf2on; }; // ---------------------------------------------------------------------------- // logstream class // Wrapper for a standard wostream with access to modified buffer // ---------------------------------------------------------------------------- class logstream : public wostream { private: // private member declarations logstream(); public: // public member declarations DblBuf *buf; explicit logstream(wstreambuf *StrBuf, bool isStd = false) : wostream(StrBuf, isStd), buf((DblBuf*)StrBuf) {} }; // ---------------------------------------------------------------------------- // Logging mode Class // ---------------------------------------------------------------------------- enum LogModes{LogToFile=1, LogToScreen, LogToBoth}; class LogMode { private: // private member declarations LogMode(); short mode; public: // public member declarations LogMode(short mode1) : mode(mode1) {} logstream& operator()(logstream &stream1) { switch(mode) { case LogToFile: stream1.buf->bf1on = true; stream1.buf->bf2on = false; break; case LogToScreen: stream1.buf->bf1on = false; stream1.buf->bf2on = true; break; case LogToBoth: stream1.buf->bf1on = true; stream1.buf->bf2on = true; } return stream1; } }; logstream& operator<<(logstream &out, LogMode mode) { return mode(out); } wostream& TimeStamp1(wostream &out1) { time_t time1; struct tm timeinfo; wchar_t timestr[512]; // Get current time and convert it to a string time(&time1); localtime_s (&timeinfo, &time1); wcsftime(timestr, 512,L"[%Y-%b-%d %H:%M:%S %p] ",&timeinfo); return out1 << timestr; } // ---------------------------------------------------------------------------- // MyLog class // Logs events to both file and screen // ---------------------------------------------------------------------------- class MyLog { private: // private member declarations MyLog(); auto_ptr<DblBuf> buf; string mErrorMsg1; string mErrorMsg2; string mErrorMsg3; string mErrorMsg4; public: // public member declarations explicit MyLog(string FileName1, wostream *ScrLog1, locale utf8locale1); ~MyLog(); void NewEvent(wstring str1, bool TimeStamp = true); string FileName; wostream *ScrLog; wofstream File; auto_ptr<logstream> Log; locale utf8locale; }; // ---------------------------------------------------------------------------- // MyLog constructor // ---------------------------------------------------------------------------- MyLog::MyLog(string FileName1, wostream *ScrLog1, locale utf8locale1) : // ctors mErrorMsg1("Failed to open file for application logging! []"), mErrorMsg2("Failed to write BOM! []"), mErrorMsg3("Failed to write to file! []"), mErrorMsg4("Failed to close file! []"), FileName(FileName1), ScrLog(ScrLog1), utf8locale(utf8locale1), File(FileName1.c_str()) { // Adjust error strings mErrorMsg1.insert(mErrorMsg1.length()-1,FileName1); mErrorMsg2.insert(mErrorMsg2.length()-1,FileName1); mErrorMsg3.insert(mErrorMsg3.length()-1,FileName1); mErrorMsg4.insert(mErrorMsg4.length()-1,FileName1); // check for file open errors if ( !File ) throw ofstream::failure(mErrorMsg1); // write UTF-8 BOM File << wchar_t(0xEF) << wchar_t(0xBB) << wchar_t(0xBF); // switch locale to UTF-8 File.imbue(utf8locale); // check for write errors if ( File.bad() ) throw ofstream::failure(mErrorMsg2); buf.reset( new DblBuf(File.rdbuf(),ScrLog->rdbuf()) ); Log.reset( new logstream(&*buf) ); } // ---------------------------------------------------------------------------- // MyLog destructor // ---------------------------------------------------------------------------- MyLog::~MyLog() { *Log << TimeStamp1 << "Log finished." << endl; // clean up objects Log.reset(); buf.reset(); File.close(); // check for file close errors if ( File.bad() ) throw ofstream::failure(mErrorMsg4); } //--------------------------------------------------------------------------- #endif // INCLUDED_MYLOG_H Tested on MSVC 2008, boost 1.42. I do not know if this is the right place to share it. Hope it helps anybody. Feel free to make it better.

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