February 2005 - Boost-users

equality fails with C++ bools
by Ross Boylan 01 Feb '05

01 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 01 Feb '05

01 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 31 Jan '05

31 Jan '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 31 Jan '05

31 Jan '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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