- Boost-users - lists.boost.org

Re: Rationale for intrusive_ptr?
by Brian Neal 02 Feb '05

02 Feb '05

Well to answer my own question, I think, it can be used when you already have something that is reference counted and you want to manage it yourself. Also in places where new and delete aren't the correct actions. Or when you need something with less resource requirements than shared_ptr. For example, when multi-threading is turned on, shared_ptr asks for a mutex. Intrusive_ptr leaves that up to you. Am I getting close here? I didn't think about using it when you have a function that takes a shared_ptr but you need to pass in this. I dunno, I tend to use shared_ptr sparingly. If I don't need a shared_ptr, I don't ask for one on the interface to a function. That way the user can pass in a naked pointer or a shared_ptr::get(). I make sure to document what the function does (and does not do) with the input pointer though. Thanks. __________________________________ Do you Yahoo!? Yahoo! Mail - Find what you need with new enhanced search. http://info.mail.yahoo.com/mail_250

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equality fails with C++ bools
by Ross Boylan 02 Feb '05

02 Feb '05

I have a function declared bool that is acting rather non-bool. std::cout << obj.fn() gives me "76" and BOOST_CHECK_EQUAL(obj.fn), true) fails, with the message /home/ross/peter/R/mspath/src/test/Covariates_test.cc(178): error in "obs_covariates": test env.matchesObservation() == true failed [76 != 1] std::cout << true prints "1". obj.fn() works OK as an argument to if (obj.fn()). I am using g++ 1:3.3.5-5 on Debian GNU/Linux. I've tried -O2 and -O1; same behavior either way. boost is 1.31.0-9 The function is declared bool matchesObservation() const Maybe bool is being typedef'd or #define'd to int somewhere, for compatibility with old code? Probably not; I tried printing typeid(xxx).name() and got "b" for true and the function return value, while I got "i" for the number 1. I tried tracing into the code with limited success. Some mix of the fact that the underlying libraries weren't a debug version, that the code was optimized, and that there are #line directives (the source files were generated out of another file) made it hard to follow. Any suggestions? -- Ross Boylan wk: (415) 502-4031 530 Parnassus Avenue (Library) rm 115-4 ross(a)biostat.ucsf.edu Dept of Epidemiology and Biostatistics fax: (415) 476-9856 University of California, San Francisco San Francisco, CA 94143-0840 hm: (415) 550-1062

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Christoph Jaeschke/Germany/IBM is out of the office.
by Christoph Jaeschke 02 Feb '05

02 Feb '05

I will be out of the office starting 02/02/2005 and will not return until 02/09/2005. I will respond to your message when I return.

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Compilation Error
by Grek 01 Feb '05

01 Feb '05

Hi: I am a newbie to the world of Boost. I have a problem in compiling a program. I do not know how to set the path to compile the attached code. My platform is Cygwin gcc version 3.3.3 The boost_1_32_0 subdirectory resides in the Cygwin directory. I tried the following, g++ boost_1_32_0/boost/graph/sourcecode.cpp and it displays the message boost/config.hpp : No such file or directory boost/graph/graph_traits.hpp : No such file or directory boost/graph/adjacency_list.hpp : No such file or directory boost/graph/dijkstra_shortest_paths.hpp : No such file or directory followed by more error messages. Please refer to the attached code and help me out. Thanks in advance. Sourcecode.cpp ****************************************************************************** #include <boost/config.hpp> #include <iostream> #include <fstream> #include <string> #include <boost/graph/graph_traits.hpp> #include <boost/graph/adjacency_list.hpp> #include <boost/graph/dijkstra_shortest_paths.hpp> using namespace boost; float maximum(float a[], float mx, int n){ float max=mx; for(int i=0; i<n; ++i){ if(max < a[i]){ max=a[i]; } } return max; } int main() { int num_nodes = 10000; int num_PPIs = 50000; char node[num_nodes][10], p1[num_PPIs][10], p2[num_PPIs][10]; char name[num_nodes]; float wt[num_PPIs], apl, dia, path[num_nodes]; int i, j, l, l1, l2, mx_len=num_nodes, pl[mx_len]; typedef adjacency_list < listS, vecS, directedS, no_property, property < edge_weight_t, float > > graph_t; typedef graph_traits < graph_t >::vertex_descriptor vertex_descriptor; typedef graph_traits < graph_t >::edge_descriptor edge_descriptor; typedef std::pair<int, int> Edge; std::ifstream INF1 ("./data/None.conversion"); std::ifstream INF2 ("./data/None.before"); if(!INF1){ std::cerr << "Cannot find INF1 file." << std::endl; return EXIT_FAILURE; } if(!INF2){ std::cerr << "Cannot find INF2 file." << std::endl; return EXIT_FAILURE; } //read data i=0; while(INF1 >> num_nodes >> node[i]){ ++i; } INF1.close(); num_nodes=i; i=0; while(INF2 >> p1[i] >> p2[i] >> wt[i]){ wt[i]=1.0; ++i; } INF2.close(); num_PPIs=i; // Edge edge_array[num_PPIs]; for(i=0; i<num_PPIs; ++i){ for(j=0; j<num_nodes; ++j){ if(stricmp(p1[i],node[j]) == 0){ edge_array[i].first=j; } } for(j=0; j<num_nodes; ++j){ if(stricmp(p2[i],node[j]) == 0){ edge_array[i].second=j; } } } // int num_arcs = sizeof(edge_array) / sizeof(Edge); std::cout << "0 None " << num_PPIs << " " << num_nodes; graph_t g(edge_array, edge_array + num_arcs, wt, num_nodes); property_map<graph_t, edge_weight_t>::type weightmap = get(edge_weight, g); std::vector<vertex_descriptor> p(num_vertices(g)); std::vector<float> d(num_vertices(g)); // l1=0; l2=0; dia=0; for(j=1; j<mx_len; ++j){ pl[j]=0; } // for(int src=0; src<num_nodes; ++src){ vertex_descriptor s = vertex(src, g); dijkstra_shortest_paths(g, s, predecessor_map(&p[0]).distance_map(&d[0])); for(j=0; j<num_nodes; ++j){ if(j == p[j]){ //set self-looping node to zero distance d[j]=0; } if(d[j] > 10000){ //set non-connecting node to zero distance d[j]=0; } path[j]=d[j]; pl[int(d[j]+0.5)]=pl[int(d[j]+0.5)]+1; } dia=maximum(path,dia,num_nodes); } for(l=1; l<=int(dia); ++l){ l1=l1+pl[l]*l; l2=l2+pl[l]; } apl=float(l1)/float(l2); std::cout << " " << apl << " " << l1 << " " << l2 << " " << dia << std::endl; return EXIT_SUCCESS; } ********************************************************************************** Cheers Grek --------------------------------- Do you Yahoo!? Yahoo! Search presents - Jib Jab's 'Second Term'

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problems with constructor/implicitly_convertible
by Benjamin Schmeling 01 Feb '05

01 Feb '05

Hi, I have defined the following: bigint* bigint_constructor(long_ l){ return new bigint(to_bigint(l)); } class_<bigint>("bigint") .def("__init__", make_constructor(bigint_constructor)) .... .... implicitly_convertible<boost::python::long_, bigint>(); Now I want to have a implicit conversion from long_ to bigint. My original c++ class has no constructor with long_ but my python-bigint class. The compiler tries to find one on c++ bigint and doesn't find it. How should I use implicitly_convertible to reach my goal? Benjamin

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Rationale for intrusive_ptr?
by Brian Neal 01 Feb '05

01 Feb '05

Hi, I need some help understanding when and why you would want to use intrusive_ptr. Does someone have an example? I didn't get much out of the current documentation for it. Thank you. __________________________________________________ Do You Yahoo!? Tired of spam? Yahoo! Mail has the best spam protection around http://mail.yahoo.com

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Two issues with lexical_cast
by Yuval Ronen 01 Feb '05

01 Feb '05

Hi. I'm probably just another one out of a million who make these remarks, but I found nothing in the documentation about them, so I'll mention them anyway. 1. lexical_cast(Source arg) takes the source argument by value. Why not by const& ? Calling lexical_cast(some_basic_string) now makes a copy of the source argument for no reason. 2. lexical_cast ignores trailing whitespaces, but not leading whitespaces. Meaning that int a = lexical_cast<int>("3 "); // three-space will work and return 3, but int a = lexical_cast<int>(" 3"); // space-three will throw. Why? There's no rationale here. Both cases should be treated in the same manner, and IMHO, that manner should be throwing. After a look at the code, it seems that the trailing-whitespace-ignore code ('stream >> std::ws' in line 151) was specifically added, so there was supposed to be a reason for this. But as I said, I believe this is wrong, at least as the default behaviour when converting a string to something else. Maybe some policies (IgnoreLeadingWhitespace, IgnoreTrailingWhitespace) can be added to control this? And again, I suppose I'm not the first to think of it... Thanks, Yuval

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RE: [Boost-users] Rationale for intrusive_ptr?
by Nat Goodspeed 01 Feb '05

01 Feb '05

> -----Original Message----- > From: boost-users-bounces(a)lists.boost.org [mailto:boost-users- > bounces(a)lists.boost.org] On Behalf Of Brian Neal > Sent: Monday, January 31, 2005 7:34 PM > To: boost-users(a)lists.boost.org > Subject: [Boost-users] Rationale for intrusive_ptr? > > Hi, I need some help understanding when and why you > would want to use intrusive_ptr. Does someone have an > example? I didn't get much out of the current > documentation for it. Thank you. [Nat] Consider: class MyClass; void some_func(const boost::shared_ptr<MyClass>& ptr); class MyClass { public: void process() { // BAD THINGS HAPPEN! some_func(boost::shared_ptr<MyClass>(this)); } }; In our current project, we've been bitten more than once :-( by situations that are analogous but less obvious. Inside a member function, you don't have a shared_ptr<MyClass>, you only have a dumb MyClass* 'this' pointer. But if MyClass is managed with smart pointers, you probably have processing functions that accept only a smart pointer to MyClass. A natural-looking data conversion is easy to code and makes the compiler happy. What happens, though, is that when you instantiate a new shared_ptr<MyClass> from your dumb 'this' pointer, it gets a whole new refcount object! In the example above, the temporary shared_ptr<> goes away as you're about to exit MyClass::process() -- which makes its spurious refcount go to 0 -- which deletes the MyClass instance in question, even though there are probably still existing shared_ptr<MyClass> references to the same instance lying around! (e.g. the one with which you called the process() method) We now use intrusive_ptr almost exclusively (vs. shared_ptr). We limit its intrusiveness by deriving all subject classes from an intrusive_base we wrote, which contains the refcount we use and a couple of methods. This practice has cut down considerably on bizarre crashes.

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implicitly_convertible<a,b>
by Benjamin Schmeling 31 Jan '05

31 Jan '05

Hi, I have exposed a bigint class which has no constructor for long_ . I added an additional constructor by defining .def("__init__", make_constructor(bigint_constructor)) This works fine. Now I want to use the implicitly_convertible function which expects from the class to have an constructor which takes the first argumen (in this case a long_) I used implicitly_convertible<boost::python::long_ ,bigint> but now the problem is that the original c++ class has no such constructor, but the wrapped class. How can I make him use my new constructor in implicitly_convertible? Benjamin

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Compile problems with multi_index on CW 9.3 (mac)?
by Marshall Clow 31 Jan '05

31 Jan '05

I'm trying to use boost::multi_index for the first time, and I'm getting odd compile errors. I have a class with two "keys", a text one and a numeric one, and I want to have two indices into the collection. So, I tried several things, and all of them get the same error: 'index_class' is not a member of class 'boost::multi_index::ordered_unique<boost::multi_index::identity<Foo>, boost::multi_index::detail::null_arg, boost::multi_index::detail::null_arg>' (and then an amazing cascade after that) Here's the basic idea: typedef boost::multi_index_container < Foo, boost::multi_index::indexed_by < boost::multi_index::ordered_unique < boost::multi_index::identity < Foo >, LessThanNumeric >, boost::multi_index::ordered_unique < boost::multi_index::identity < Foo >, LessThanText > > > Foo_; where LessThanNumeric (and LessThanText, too) looks like this: struct LessThanNumeric: std::binary_function< Foo, Foo, bool > { bool operator () ( const Foo& x, const Foo& y ) const { return x.NumericKey () < y.NumericKey (); } }; My source is at <http://www.idio.com/misc/mi-test.cpp> Anyone got any tips? Thanks! -- -- Marshall Marshall Clow Idio Software <mailto:marshall@idio.com> It is by caffeine alone I set my mind in motion. It is by the beans of Java that thoughts acquire speed, the hands acquire shaking, the shaking becomes a warning. It is by caffeine alone I set my mind in motion.

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