you could use "open" to try to open the stream as described here http://www.cplusplus.com/reference/fstream/fstream/open/
I'll do a small test to see -Pedro ----- Original Message ----- From: "Pedro Vicente" <pedro.vice...@space-research.org> To: "Alan W. Irwin" <ir...@beluga.phys.uvic.ca>; "Phil Rosenberg" <p.d.rosenb...@gmail.com>; "PLplot development list" <plplot-devel@lists.sourceforge.net> Sent: Monday, December 19, 2016 8:30 PM Subject: Re: [Plplot-devel] New way to generate wxwidgets debug output > Hi Alan > > > ok, I see now. > >> That is check if >> >> std::fstream fin( "/dev/urandom", std::ios::in ); > > > this is the constructor, there is no return value, which is one of the > criticisms made to C++. > > In this case probably you need to do a small I/O operation after that call > and check for the result. > > Not sure which , because I never use the C++ I/O, I always use the C API, > even in C++ programs. > > the reference is here > > http://www.cplusplus.com/reference/fstream/fstream/fstream/ > > > -Pedro > > > > ----- Original Message ----- > From: "Alan W. Irwin" <ir...@beluga.phys.uvic.ca> > To: "Pedro Vicente" <pedro.vice...@space-research.org>; "Phil Rosenberg" > <p.d.rosenb...@gmail.com>; "PLplot development list" > <plplot-devel@lists.sourceforge.net> > Sent: Monday, December 19, 2016 7:51 PM > Subject: RE: New way to generate wxwidgets debug output > > >> On 2016-12-19 16:33-0500 Pedro Vicente wrote: >> >>> Hi Alan >>> >>> >>>> The only trouble with the above fix is not every Unix platform has >>>> /dev/urandom (although from the above URL most do). >>>> >>>> So I would like to change the above fix to check for /dev/urandom >>>> and use it if it exists, but otherwise fall back to using /dev/random. >>>> >>>> How do I do that in C++? >>> >>> >>> This is not a C++ (or C) issue. >>> This is ideal for cmake to check, the same way it detects for other >>> possible system functions/features availability. >>> I never did this before, but I think the way it works it is on the cmake >>> script >>> do a small C or C++ program embedded in the script that includes >>> "/dev/urandom" in some way, for example >>> >>> std::fstream fin( "/dev/urandom", std::ios::in ); >>> >>> and then check if it compiles and pass the result to cmake >>> >>>> > /dev/urandom (although from the above URL most do). >> >> Hi Pedro: >> >> I agree that is a possible approach, but that would mean >> I would need to implement a build-system CMake test, propagate the >> relevant CMake variable from that test >> to the C++ level as a macro, and introduce a preprocessor directive into >> our own C++ >> code based on whether that macro is defined or not. And I think my >> original proposal is simpler than that. >> >> I never stated clearly what my proposed approach >> would be, but it is no coincidence that it is C like. :-) >> >> That is check if >> >> std::fstream fin( "/dev/urandom", std::ios::in ); >> >> works (probably by just checking the return code of that call, but I >> could not find the documentation of what the return code would be >> on failure), >> >> and if that return code indicates a failure, then call >> >> std::fstream fin( "/dev/random", std::ios::in ); >> >> instead. But I assume Phil will do (or has done by now) the >> equivalent using C++ exception handling. >> >> Alan >> __________________________ >> Alan W. Irwin >> >> Astronomical research affiliation with Department of Physics and >> Astronomy, >> University of Victoria (astrowww.phys.uvic.ca). >> >> Programming affiliations with the FreeEOS equation-of-state >> implementation for stellar interiors (freeeos.sf.net); the Time >> Ephemerides project (timeephem.sf.net); PLplot scientific plotting >> software package (plplot.sf.net); the libLASi project >> (unifont.org/lasi); the Loads of Linux Links project (loll.sf.net); >> and the Linux Brochure Project (lbproject.sf.net). >> __________________________ >> >> Linux-powered Science >> __________________________ >> > > > ------------------------------------------------------------------------------ > Developer Access Program for Intel Xeon Phi Processors > Access to Intel Xeon Phi processor-based developer platforms. > With one year of Intel Parallel Studio XE. > Training and support from Colfax. > Order your platform today.http://sdm.link/intel > _______________________________________________ > Plplot-devel mailing list > Plplot-devel@lists.sourceforge.net > https://lists.sourceforge.net/lists/listinfo/plplot-devel > ------------------------------------------------------------------------------ Developer Access Program for Intel Xeon Phi Processors Access to Intel Xeon Phi processor-based developer platforms. With one year of Intel Parallel Studio XE. Training and support from Colfax. Order your platform today.http://sdm.link/intel _______________________________________________ Plplot-devel mailing list Plplot-devel@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/plplot-devel
