February 2003 - Boost-users

date_time problems
by Eric Crampton 25 Feb '03

25 Feb '03

I'm trying to test the date_time functionality of boost and am having some difficulties. I would like to simply get the current local time into a ptime and write it out as an ISO-8601 string. Using Boost 1.29 and g++ 3.2, when I compile the following code I get a number of *linker* errors. Code: #include <boost/date_time/posix_time/posix_time_types.hpp> #include <boost/date_time/posix_time/time_formatters.hpp> int main() { boost::posix_time::ptime pt = boost::posix_time::second_clock::local_time(); std::cout << boost::posix_time::to_iso_extended_string(pt) << std::endl; } That code seems pretty straightforward to me. The linker errors look like the following: test.cpp:7: undefined reference to `boost::date_time::gregorian_calendar_base<boost::date_time::year_month_day_base<boost::gregorian::greg_year, boost::gregorian::greg_month, boost::gregorian::greg_day>, unsigned long>::day_number(boost::date_time::year_month_day_base<boost::gregorian::greg_year, boost::gregorian::greg_month, boost::gregorian::greg_day> const&)' test.cpp:6: undefined reference to `boost::date_time::gregorian_calendar_base<boost::date_time::year_month_day_base<boost::gregorian::greg_year, boost::gregorian::greg_month, boost::gregorian::greg_day>, unsigned long>::from_day_number(unsigned long)' (snipped...) Best as I can tell (cd $BOOST_ROOT/boost/date_time && find . -name '*.cpp' -print), there are no .cpp files to be compiled... Anyone know what's up? --Eric _________________________________________________________________ Protect your PC - get McAfee.com VirusScan Online http://clinic.mcafee.com/clinic/ibuy/campaign.asp?cid=3963

4 3

Please help! Problem with histogram.cpp needed for project.
by agiatojon <JonAgiato＠nyc.rr.com> 25 Feb '03

25 Feb '03

Hello all, I have been unable to successfully compile histogram.cpp in the random library folder, version 1_29_0, using Visual Studio.NET. I obtain the following errors: c:\Documents and Settings\Agiato\My Documents\Visual Studio Projects\histogramTest\driver.cpp(49): warning C4267: 'argument' : conversion from 'size_t' to 'std::streamsize', possible loss of data c:\Documents and Settings\Agiato\My Documents\Visual Studio Projects\histogramTest\driver.cpp(97): error C2061: syntax error : identifier 'base' c:\Documents and Settings\Agiato\My Documents\Visual Studio Projects\histogramTest\driver.cpp(97): error C2066: cast to function type is illegal c:\Documents and Settings\Agiato\My Documents\Visual Studio Projects\histogramTest\driver.cpp(97): error C2059: syntax error : ')' c:\Documents and Settings\Agiato\My Documents\Visual Studio Projects\histogramTest\driver.cpp(101): error C2065: 'gen' : undeclared identifier c:\Documents and Settings\Agiato\My Documents\Visual Studio Projects\histogramTest\driver.cpp(111): error C2228: left of '.base' must have class/struct/union type c:\Documents and Settings\Agiato\My Documents\Visual Studio Projects\histogramTest\driver.cpp(111): error C2228: left of '.sum' must have class/struct/union type c:\Documents and Settings\Agiato\My Documents\Visual Studio Projects\histogramTest\driver.cpp(113): error C2228: left of '.squaresum' must have class/struct/union type c:\Documents and Settings\Agiato\My Documents\Visual Studio Projects\histogramTest\driver.cpp(97): error C2061: syntax error : identifier 'base' c:\Documents and Settings\Agiato\My Documents\Visual Studio Projects\histogramTest\driver.cpp(97): error C2066: cast to function type is illegal c:\Documents and Settings\Agiato\My Documents\Visual Studio Projects\histogramTest\driver.cpp(97): error C2059: syntax error : ')' c:\Documents and Settings\Agiato\My Documents\Visual Studio Projects\histogramTest\driver.cpp(111): error C2228: left of '.base' must have class/struct/union type c:\Documents and Settings\Agiato\My Documents\Visual Studio Projects\histogramTest\driver.cpp(111): error C2228: left of '.sum' must have class/struct/union type c:\Documents and Settings\Agiato\My Documents\Visual Studio Projects\histogramTest\driver.cpp(113): error C2228: left of '.squaresum' must have class/struct/union type c:\Documents and Settings\Agiato\My Documents\Visual Studio Projects\histogramTest\driver.cpp(97): error C2061: syntax error : identifier 'base' c:\Documents and Settings\Agiato\My Documents\Visual Studio Projects\histogramTest\driver.cpp(97): error C2066: cast to function type is illegal c:\Documents and Settings\Agiato\My Documents\Visual Studio Projects\histogramTest\driver.cpp(97): error C2059: syntax error : ')' c:\Documents and Settings\Agiato\My Documents\Visual Studio Projects\histogramTest\driver.cpp(111): error C2228: left of '.base' must have class/struct/union type c:\Documents and Settings\Agiato\My Documents\Visual Studio Projects\histogramTest\driver.cpp(111): error C2228: left of '.sum' must have class/struct/union type c:\Documents and Settings\Agiato\My Documents\Visual Studio Projects\histogramTest\driver.cpp(113): error C2228: left of '.squaresum' must have class/struct/union type c:\Documents and Settings\Agiato\My Documents\Visual Studio Projects\histogramTest\driver.cpp(97): error C2061: syntax error : identifier 'base' c:\Documents and Settings\Agiato\My Documents\Visual Studio Projects\histogramTest\driver.cpp(97): error C2066: cast to function type is illegal c:\Documents and Settings\Agiato\My Documents\Visual Studio Projects\histogramTest\driver.cpp(97): error C2059: syntax error : ')' c:\Documents and Settings\Agiato\My Documents\Visual Studio Projects\histogramTest\driver.cpp(111): error C2228: left of '.base' must have class/struct/union type c:\Documents and Settings\Agiato\My Documents\Visual Studio Projects\histogramTest\driver.cpp(111): error C2228: left of '.sum' must have class/struct/union type c:\Documents and Settings\Agiato\My Documents\Visual Studio Projects\histogramTest\driver.cpp(113): error C2228: left of '.squaresum' must have class/struct/union type c:\Documents and Settings\Agiato\My Documents\Visual Studio Projects\histogramTest\driver.cpp(97): error C2061: syntax error : identifier 'base' c:\Documents and Settings\Agiato\My Documents\Visual Studio Projects\histogramTest\driver.cpp(97): error C2066: cast to function type is illegal c:\Documents and Settings\Agiato\My Documents\Visual Studio Projects\histogramTest\driver.cpp(97): error C2059: syntax error : ')' c:\Documents and Settings\Agiato\My Documents\Visual Studio Projects\histogramTest\driver.cpp(111): error C2228: left of '.base' must have class/struct/union type c:\Documents and Settings\Agiato\My Documents\Visual Studio Projects\histogramTest\driver.cpp(111): error C2228: left of '.sum' must have class/struct/union type c:\Documents and Settings\Agiato\My Documents\Visual Studio Projects\histogramTest\driver.cpp(113): error C2228: left of '.squaresum' must have class/struct/union type c:\Documents and Settings\Agiato\My Documents\Visual Studio Projects\histogramTest\driver.cpp(97): error C2061: syntax error : identifier 'base' c:\Documents and Settings\Agiato\My Documents\Visual Studio Projects\histogramTest\driver.cpp(97): error C2066: cast to function type is illegal c:\Documents and Settings\Agiato\My Documents\Visual Studio Projects\histogramTest\driver.cpp(97): error C2059: syntax error : ')' c:\Documents and Settings\Agiato\My Documents\Visual Studio Projects\histogramTest\driver.cpp(111): error C2228: left of '.base' must have class/struct/union type c:\Documents and Settings\Agiato\My Documents\Visual Studio Projects\histogramTest\driver.cpp(111): error C2228: left of '.sum' must have class/struct/union type c:\Documents and Settings\Agiato\My Documents\Visual Studio Projects\histogramTest\driver.cpp(113): error C2228: left of '.squaresum' must have class/struct/union type c:\Documents and Settings\Agiato\My Documents\Visual Studio Projects\histogramTest\driver.cpp(97): error C2061: syntax error : identifier 'base' c:\Documents and Settings\Agiato\My Documents\Visual Studio Projects\histogramTest\driver.cpp(97): error C2066: cast to function type is illegal c:\Documents and Settings\Agiato\My Documents\Visual Studio Projects\histogramTest\driver.cpp(97): error C2059: syntax error : ')' c:\Documents and Settings\Agiato\My Documents\Visual Studio Projects\histogramTest\driver.cpp(111): error C2228: left of '.base' must have class/struct/union type c:\Documents and Settings\Agiato\My Documents\Visual Studio Projects\histogramTest\driver.cpp(111): error C2228: left of '.sum' must have class/struct/union type c:\Documents and Settings\Agiato\My Documents\Visual Studio Projects\histogramTest\driver.cpp(113): error C2228: left of '.squaresum' must have class/struct/union type c:\Documents and Settings\Agiato\My Documents\Visual Studio Projects\histogramTest\driver.cpp(97): error C2061: syntax error : identifier 'base' c:\Documents and Settings\Agiato\My Documents\Visual Studio Projects\histogramTest\driver.cpp(97): error C2066: cast to function type is illegal c:\Documents and Settings\Agiato\My Documents\Visual Studio Projects\histogramTest\driver.cpp(97): error C2059: syntax error : ')' c:\Documents and Settings\Agiato\My Documents\Visual Studio Projects\histogramTest\driver.cpp(111): error C2228: left of '.base' must have class/struct/union type c:\Documents and Settings\Agiato\My Documents\Visual Studio Projects\histogramTest\driver.cpp(111): error C2228: left of '.sum' must have class/struct/union type c:\Documents and Settings\Agiato\My Documents\Visual Studio Projects\histogramTest\driver.cpp(113): error C2228: left of '.squaresum' must have class/struct/union type It appears to me that all of these messages will go away when the second one, c:\Documents and Settings\Agiato\My Documents\Visual Studio Projects\histogramTest\driver.cpp(97): error C2061: syntax error : identifier 'base', is corrected. Any assistance is greatly appreciated! Thank you. Jon Agiato JonAgiato(a)nyc.rr.com

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Is implicit casting with boost::any possible?
by Matthew Dempsky 25 Feb '03

25 Feb '03

I'm curious if there's any way to get code like the following to work: boost::any a = char(10); int i = boost::any_cast<int>(a); More specifically, what I mean is, I'd like to be able to place a value of type T1 in 'a' and then retrieve it as type T2 which it can be implicitly cast to. Is this possible without the part that extracts the value from 'a' adding a lot of extra code to test all possibilities? What I would like to do is fill a map<string, any> with function pointers/objects/etc. and pass it to a function which casts the any values to slot types to connect to different signals whose type is determined at runtime. Basically something like this (but with MySig an unknown type until runtime). int func(char c, int i = 10); boost::any a = &func; typedef boost::signal<void (char)> MySig; MySig sig; sig.connect(boost::any_cast<MySig::slot_type>(a)); sig('j'); -jivera

2 1

C++ object from PyObject pointer
by mghiggins <mghiggins＠yahoo.com> 24 Feb '03

24 Feb '03

Excuse my newbiness if this question is too dumb... :) I've built a python extension from a C++ class using boost - it all seems to work fine. However, now another C++ function is receiving a pointer to a PyObject that represents an instance of this "boosted" python class. How do I pick off a pointer to the underlying C++ object from the PyObject pointer?

2 1

Re: [Boost-Users] lexical_cast bug.
by Terje Slettebø 23 Feb '03

23 Feb '03

>From: "Eduardo Chao" <efchao(a)hotmail.com> > I am a new suscriber to the list. > I want to report what I consider a bug in lexical_cast conversion template. > First, I wanted to use it to convert things to std::string (Target). > It throws a bad_lexical_cast_exception when I pass an empty std::string object (one > that is default-constructed or constructed with "") as the Source argument. > It throws it because the condition (interpreter >> result ) evaluates to > false. Yes, this is a bug in the current version, see (http://www.boost.org/libs/conversion/lexical_cast.htm#future) There's a proposition which fixes this and other problems here (http://groups.yahoo.com/group/boost/files/lexical_cast_proposition/lexical_ cast_proposition.zip). It's scheduled to be reviewed by the author, Kevlin Henney, or Björn Karlsson (Boost's maintenance wizard), before Boost release 1.30. If they find it ok, a notice will also be posted at the Boost list, so that others may give feedback before the release, as well. > My solution was to specialize the function template this way: > > template<> lexical_cast<std::string>(const std::string &str) > { > return str; > } The proposition handles it in a similar way. However, it's not possible to partially specialise function templates (e.g. to handle all T -> std::basic_string conversions), so function template overloading is used, instead. This is because it needs to handle conversion from any type to std::basic_string, as there may be other types which output empty strings or whitespace, as well. > but it is not so general to support const std::string or const std::string& > as Target type or perhaps std::string or const std::string etc as Source. > Correct me if I am wrong, so I learn from you more experienced Boost (and then C++) users. No, you're right. However, it's only necessary to handle T -> std::basic_string (not cv-qualification or reference) in this case, because: lexical_cast<std::string>(...); // Ok lexical_cast<const std::string>(...); // Error, can't write to a const string lexical_cast<const std::string &>(...); // Error, can't return a reference to the result (it would then return a dangling reference, as the result would be a temporary) lexical_cast<std::string>(const_cast<const std::string>(...)); // Ok, top-level cv-qualifiers are ignored when matching the call Regards, Terje

1 0

random/histogram.cpp
by agiatojon <JonAgiato＠nyc.rr.com> 23 Feb '03

23 Feb '03

Hello all, I have been unable to successfully compile histogram.cpp in the random library folder, version 1_29_0, using Visual Studio.NET. I obtain the following errors: c:\Documents and Settings\Agiato\My Documents\Visual Studio Projects\histogramTest\driver.cpp(49): warning C4267: 'argument' : conversion from 'size_t' to 'std::streamsize', possible loss of data c:\Documents and Settings\Agiato\My Documents\Visual Studio Projects\histogramTest\driver.cpp(97): error C2061: syntax error : identifier 'base' c:\Documents and Settings\Agiato\My Documents\Visual Studio Projects\histogramTest\driver.cpp(97): error C2066: cast to function type is illegal c:\Documents and Settings\Agiato\My Documents\Visual Studio Projects\histogramTest\driver.cpp(97): error C2059: syntax error : ')' c:\Documents and Settings\Agiato\My Documents\Visual Studio Projects\histogramTest\driver.cpp(101): error C2065: 'gen' : undeclared identifier c:\Documents and Settings\Agiato\My Documents\Visual Studio Projects\histogramTest\driver.cpp(111): error C2228: left of '.base' must have class/struct/union type c:\Documents and Settings\Agiato\My Documents\Visual Studio Projects\histogramTest\driver.cpp(111): error C2228: left of '.sum' must have class/struct/union type c:\Documents and Settings\Agiato\My Documents\Visual Studio Projects\histogramTest\driver.cpp(113): error C2228: left of '.squaresum' must have class/struct/union type c:\Documents and Settings\Agiato\My Documents\Visual Studio Projects\histogramTest\driver.cpp(97): error C2061: syntax error : identifier 'base' c:\Documents and Settings\Agiato\My Documents\Visual Studio Projects\histogramTest\driver.cpp(97): error C2066: cast to function type is illegal c:\Documents and Settings\Agiato\My Documents\Visual Studio Projects\histogramTest\driver.cpp(97): error C2059: syntax error : ')' c:\Documents and Settings\Agiato\My Documents\Visual Studio Projects\histogramTest\driver.cpp(111): error C2228: left of '.base' must have class/struct/union type c:\Documents and Settings\Agiato\My Documents\Visual Studio Projects\histogramTest\driver.cpp(111): error C2228: left of '.sum' must have class/struct/union type c:\Documents and Settings\Agiato\My Documents\Visual Studio Projects\histogramTest\driver.cpp(113): error C2228: left of '.squaresum' must have class/struct/union type c:\Documents and Settings\Agiato\My Documents\Visual Studio Projects\histogramTest\driver.cpp(97): error C2061: syntax error : identifier 'base' c:\Documents and Settings\Agiato\My Documents\Visual Studio Projects\histogramTest\driver.cpp(97): error C2066: cast to function type is illegal c:\Documents and Settings\Agiato\My Documents\Visual Studio Projects\histogramTest\driver.cpp(97): error C2059: syntax error : ')' c:\Documents and Settings\Agiato\My Documents\Visual Studio Projects\histogramTest\driver.cpp(111): error C2228: left of '.base' must have class/struct/union type c:\Documents and Settings\Agiato\My Documents\Visual Studio Projects\histogramTest\driver.cpp(111): error C2228: left of '.sum' must have class/struct/union type c:\Documents and Settings\Agiato\My Documents\Visual Studio Projects\histogramTest\driver.cpp(113): error C2228: left of '.squaresum' must have class/struct/union type c:\Documents and Settings\Agiato\My Documents\Visual Studio Projects\histogramTest\driver.cpp(97): error C2061: syntax error : identifier 'base' c:\Documents and Settings\Agiato\My Documents\Visual Studio Projects\histogramTest\driver.cpp(97): error C2066: cast to function type is illegal c:\Documents and Settings\Agiato\My Documents\Visual Studio Projects\histogramTest\driver.cpp(97): error C2059: syntax error : ')' c:\Documents and Settings\Agiato\My Documents\Visual Studio Projects\histogramTest\driver.cpp(111): error C2228: left of '.base' must have class/struct/union type c:\Documents and Settings\Agiato\My Documents\Visual Studio Projects\histogramTest\driver.cpp(111): error C2228: left of '.sum' must have class/struct/union type c:\Documents and Settings\Agiato\My Documents\Visual Studio Projects\histogramTest\driver.cpp(113): error C2228: left of '.squaresum' must have class/struct/union type c:\Documents and Settings\Agiato\My Documents\Visual Studio Projects\histogramTest\driver.cpp(97): error C2061: syntax error : identifier 'base' c:\Documents and Settings\Agiato\My Documents\Visual Studio Projects\histogramTest\driver.cpp(97): error C2066: cast to function type is illegal c:\Documents and Settings\Agiato\My Documents\Visual Studio Projects\histogramTest\driver.cpp(97): error C2059: syntax error : ')' c:\Documents and Settings\Agiato\My Documents\Visual Studio Projects\histogramTest\driver.cpp(111): error C2228: left of '.base' must have class/struct/union type c:\Documents and Settings\Agiato\My Documents\Visual Studio Projects\histogramTest\driver.cpp(111): error C2228: left of '.sum' must have class/struct/union type c:\Documents and Settings\Agiato\My Documents\Visual Studio Projects\histogramTest\driver.cpp(113): error C2228: left of '.squaresum' must have class/struct/union type c:\Documents and Settings\Agiato\My Documents\Visual Studio Projects\histogramTest\driver.cpp(97): error C2061: syntax error : identifier 'base' c:\Documents and Settings\Agiato\My Documents\Visual Studio Projects\histogramTest\driver.cpp(97): error C2066: cast to function type is illegal c:\Documents and Settings\Agiato\My Documents\Visual Studio Projects\histogramTest\driver.cpp(97): error C2059: syntax error : ')' c:\Documents and Settings\Agiato\My Documents\Visual Studio Projects\histogramTest\driver.cpp(111): error C2228: left of '.base' must have class/struct/union type c:\Documents and Settings\Agiato\My Documents\Visual Studio Projects\histogramTest\driver.cpp(111): error C2228: left of '.sum' must have class/struct/union type c:\Documents and Settings\Agiato\My Documents\Visual Studio Projects\histogramTest\driver.cpp(113): error C2228: left of '.squaresum' must have class/struct/union type c:\Documents and Settings\Agiato\My Documents\Visual Studio Projects\histogramTest\driver.cpp(97): error C2061: syntax error : identifier 'base' c:\Documents and Settings\Agiato\My Documents\Visual Studio Projects\histogramTest\driver.cpp(97): error C2066: cast to function type is illegal c:\Documents and Settings\Agiato\My Documents\Visual Studio Projects\histogramTest\driver.cpp(97): error C2059: syntax error : ')' c:\Documents and Settings\Agiato\My Documents\Visual Studio Projects\histogramTest\driver.cpp(111): error C2228: left of '.base' must have class/struct/union type c:\Documents and Settings\Agiato\My Documents\Visual Studio Projects\histogramTest\driver.cpp(111): error C2228: left of '.sum' must have class/struct/union type c:\Documents and Settings\Agiato\My Documents\Visual Studio Projects\histogramTest\driver.cpp(113): error C2228: left of '.squaresum' must have class/struct/union type c:\Documents and Settings\Agiato\My Documents\Visual Studio Projects\histogramTest\driver.cpp(97): error C2061: syntax error : identifier 'base' c:\Documents and Settings\Agiato\My Documents\Visual Studio Projects\histogramTest\driver.cpp(97): error C2066: cast to function type is illegal c:\Documents and Settings\Agiato\My Documents\Visual Studio Projects\histogramTest\driver.cpp(97): error C2059: syntax error : ')' c:\Documents and Settings\Agiato\My Documents\Visual Studio Projects\histogramTest\driver.cpp(111): error C2228: left of '.base' must have class/struct/union type c:\Documents and Settings\Agiato\My Documents\Visual Studio Projects\histogramTest\driver.cpp(111): error C2228: left of '.sum' must have class/struct/union type c:\Documents and Settings\Agiato\My Documents\Visual Studio Projects\histogramTest\driver.cpp(113): error C2228: left of '.squaresum' must have class/struct/union type It appears to me that all of these messages will go away when the second one, c:\Documents and Settings\Agiato\My Documents\Visual Studio Projects\histogramTest\driver.cpp(97): error C2061: syntax error : identifier 'base', is corrected. Any assistance is greatly apprechiated! Thank you. Jon Agiato JonAgiato(a)nyc.rr.com

1 0

[BGL] Using external edge properties
by yg-boost-users＠m.gmane.org 22 Feb '03

22 Feb '03

I have a graph which might change during it's lifetime. I want to attach external properties to this graph. Now, it seems like that in order to be able to attach external properties, I need to have an internal property with edge indices, ie that enumerates the edges. These indices need to be continuous as I gather, since they are used to index for instance a vector of num_edges() elements. Does this mean that I have to re-enumerate all edges if I remove one? This seems to me very cumbersome and also time consuming if the graph is large and changes a lot. Is there another way? Björn Lindberg

2 2

bug in shared_ptr
by Simone Finotti 22 Feb '03

22 Feb '03

hi all, I don't know if this is the right place to report bug, if it's not please forgive me. I was trying to use boost/shared_ptr.hpp class, so I defined BOOST_NO_EXCEPTIONS because my compiler doesn't support C++ exceptions, but I receive this error: ..\..\boost_1_29_0\boost/detail/shared_count.hpp(122) : error C2039: 'use_count_is_zero' : is not a member of 'boost' ..\..\boost_1_29_0\boost/detail/shared_count.hpp(122) : error C2065: 'use_count_is_zero' : undeclared identifier in detail, here's an excerpt from shared_count.hpp, where the compiler gives the error: void add_ref() { #ifdef BOOST_HAS_THREADS mutex_type::scoped_lock lock(mtx_); #endif if(use_count_ == 0 && weak_count_ != 0) boost::throw_exception(boost::use_count_is_zero()); ++use_count_; ++weak_count_; } use_count_is_zero is not defined because it's defined, in the same file, as: #ifndef BOOST_NO_EXCEPTIONS class use_count_is_zero: public std::exception { public: virtual char const * what() const throw() { return "boost::use_count_is_zero"; } }; #endif is there a way to make it work? -- Simone

2 1

Can one "nest" regular expressions ?
by yg-boost-users＠m.gmane.org 22 Feb '03

22 Feb '03

Hello folks, I believe my question applies to regular expression libraries generally and not just to regexp++. I want to know if it is possible to refer to or use one regular expression within another. What I wish to do is parse a string of html code for img tags, and if they have the clause ALT="whatever" replace the whole image tag with 'whatever'. So I decided to make regular expression for an image tag which had an ALT part, and have a sub-match on the contents of quoted part of the ALT. (I broke this up a bit, explaining what each part is for . . .) This will match img tags: static const boost::regex find_imgs(" <\\s*img Matches <, 0 or many whitespace, IMG \\s+src\\s* Matches 1 or more whitespace, SRC, 0 or many whitespace =\\s* Matches = followed by 0 or more whitespace \"\\s* Matches " followed by 0 or more whitespace ([^\"]*) Matches any number of characters that are not " ([^>]*>) Matches any number of chars that not >, followed by a > ", boost::regbase::normal | boost::regbase::icase); Ok, so now look at this one. I'm trying to do the same as above except I want to sub-match the quoted part of the alt part so I can use it. I can't do "anything except the word 'alt'" because it will interpret the [^(alt)] as "anything except 'a', 'l', or 't'". static const boost::regex find_imgs_with_alt(" <\\s*img Matches <, 0 or many whitespace, IMG \\s+src\\s* Matches 1 or more whitespace, SRC, 0 or many whitespace =\\s* Matches = followed by 0 or more whitespace \"\\s* Matches " followed by 0 or more whitespace [^\"]* Matches any number of chars not " \\s+ Matches 1 or more whitespace [^alt]* I would like match anything except the word ALT, but the regexp stuff interprets this as anything but 'a', 'l', or 't' alt\\s*= Matches ALT, 0 or whitespace, = \"(^\")\" Matches ", anything except a " as a group that I can reference, then another " [^>]*> Matches any number of chars not >, followed by a > ", boost::regbase::normal | boost::regbase::icase); So what I want to do is make another regular expression which matches "alt", and in the part that says [^alt]* do instead something like [^@alt]* where '@' would indicate that 'alt' was the name of another regular expression, such as static const boost::regex alt("alt", boost::regbase::normal | boost::regbase::icase); I can see how to do what I want to do without this; I would get the whole IMG tag and do a separate regexp_search on the match. But it seems to make it so much easier if it were possible, especially leaving me with fewer lines of regular expression code to have bugs in. If this is possible I'd like to know. Thanks in advance, and I'll post the regular expressions I end up using here if anyone might find them of use. --Rob

4 9

lexical_cast bug.
by Eduardo Chao 22 Feb '03

22 Feb '03

Hello, I am a new suscriber to the list. I want to report what I consider a bug in lexical_cast conversion template. First, I wanted to use it to convert things to std::string (Target). It throws a bad_lexical_cast_exception when I pass an empty std::string object (one that is default-constructed or constructed with "") as the Source argument. It throws it because the condition (interpreter >> result ) evaluates to false. My solution was to specialize the function template this way: template<> lexical_cast<std::string>(const std::string &str) { return str; } but it is not so general to support const std::string or const std::string& as Target type or perhaps std::string or const std::string etc as Source. Correct me if I am wrong, so I learn from you more experienced Boost (and then C++) users. That's all for now. Thanks in advance. Eduardo Chao. [Non-text portions of this message have been removed]

1 0