(Boost.Python) How to print from C++ to the same stream as Python's 'print' does?
Hi, I would like to print from C++ to the same stream as Python's 'print' command does. I am using an embedded Python shell and when using std::cout nothing is printed at all... Currently I am using the following code: std::ostringstream oss; oss << "test\n"; std::string cs = oss.str(); PySys_WriteStdout(cs.c_str()); I wonder if there is an easier way to get the same result? Thanks, Dietrich
This is very old and probably largely wrong by now, but the general concept is the same. http://www.respower.com/~earlye/programming/19991206.001.htm Basically, you need to create a streambuf class that calls PySys_WriteStdout() inside your_streambuf_class::sync(). -- Early Ehlinger On Mon, May 11, 2009 at 11:11 AM, Dietrich Bollmann <diresu@web.de> wrote:
Hi,
I would like to print from C++ to the same stream as Python's 'print' command does. I am using an embedded Python shell and when using std::cout nothing is printed at all...
Currently I am using the following code:
std::ostringstream oss; oss << "test\n"; std::string cs = oss.str(); PySys_WriteStdout(cs.c_str());
I wonder if there is an easier way to get the same result?
Thanks, Dietrich
_______________________________________________ Boost-users mailing list Boost-users@lists.boost.org http://lists.boost.org/mailman/listinfo.cgi/boost-users
-- Early Ehlinger
On Mon, May 11, 2009 at 2:17 PM, Early Ehlinger <earlye@gmail.com> wrote:
Basically, you need to create a streambuf class that calls PySys_WriteStdout() inside your_streambuf_class::sync().
It's probably fairly straightforward to do this using Boost.Iostreams, by creating a model of Sink: include <Python.h> #include <algorithm> // min #include <iosfwd> // streamsize #include <boost/iostreams/categories.hpp> // sink_tag #include <boost/iostreams/stream.hpp> // stream #include <boost/format.hpp> // format class pysys_stdout_sink { public: typedef char char_type; typedef boost::iostreams::sink_tag category; std::streamsize write( const char* s, std::streamsize n ) { // PySys_WriteStdout truncates to 1000 chars static const std::streamsize MAXSIZE = 1000; std::streamsize written = std::min( n, MAXSIZE ); PySys_WriteStdout( (boost::format("%%.%1%s") % written).str().c_str(), s ); return written; } }; boost::iostreams::stream<pysys_stdout_sink> pysys_stdout; int main() { Py_Initialize(); pysys_stdout << "Hello, Python world!\n"; } HTH, Christopher
I don't know if that helps the OP, but it's certainly an improvement over mine! Thanks. -- Early On Wed, May 13, 2009 at 3:11 AM, Christopher Currie <christopher@currie.com>wrote:
On Mon, May 11, 2009 at 2:17 PM, Early Ehlinger <earlye@gmail.com> wrote:
Basically, you need to create a streambuf class that calls PySys_WriteStdout() inside your_streambuf_class::sync().
It's probably fairly straightforward to do this using Boost.Iostreams, by creating a model of Sink:
include <Python.h>
#include <algorithm> // min #include <iosfwd> // streamsize #include <boost/iostreams/categories.hpp> // sink_tag #include <boost/iostreams/stream.hpp> // stream #include <boost/format.hpp> // format
class pysys_stdout_sink { public: typedef char char_type; typedef boost::iostreams::sink_tag category;
std::streamsize write( const char* s, std::streamsize n ) { // PySys_WriteStdout truncates to 1000 chars static const std::streamsize MAXSIZE = 1000;
std::streamsize written = std::min( n, MAXSIZE ); PySys_WriteStdout( (boost::format("%%.%1%s") % written).str().c_str(), s );
return written; } };
boost::iostreams::stream<pysys_stdout_sink> pysys_stdout;
int main() { Py_Initialize(); pysys_stdout << "Hello, Python world!\n"; }
HTH, Christopher _______________________________________________ Boost-users mailing list Boost-users@lists.boost.org http://lists.boost.org/mailman/listinfo.cgi/boost-users
-- Early Ehlinger
Hi Christopher and Early, ...I thought there is some standard Boost.Python stream somewhere anyway and didn't expect this kind of solution :) The code became longer than before (at least when calculating the definition of the sink class also) - but much more elegant :) Before: std::ostringstream oss; oss << "Hello, Python world!" << std::endl; std::string cs = oss.str(); PySys_WriteStdout(cs.c_str()); Now: boost::iostreams::stream<pysys_stdout_sink> pysys_stdout; pysys_stdout.open(pysys_stdout_sink()); pysys_stdout << "Hello, Python world!" << std::endl; (I had to add the line: pysys_stdout.open(pysys_stdout_sink()); to make it work.) Thank you very much for your help, Dietrich --- Here the code to play around with on unix/linux - maybe it is helpful for some other person with the same problem: mkdir -p /tmp/pysys_stdout cd /tmp/pysys_stdout cat > pysys_stdout.cpp <<FIN /* pysys_stdout.cpp */ #include <python2.5/Python.h> #include <algorithm> // min #include <iosfwd> // streamsize #include <boost/iostreams/categories.hpp> // sink_tag #include <boost/iostreams/stream.hpp> // stream #include <boost/format.hpp> // format class pysys_stdout_sink { public: typedef char char_type; typedef boost::iostreams::sink_tag category; std::streamsize write( const char* s, std::streamsize n ) { // PySys_WriteStdout truncates to 1000 chars static const std::streamsize MAXSIZE = 1000; std::streamsize written = std::min( n, MAXSIZE ); PySys_WriteStdout( (boost::format("%%.%1%s") % written).str().c_str(), s ); return written; } }; boost::iostreams::stream<pysys_stdout_sink> pysys_stdout; int main() { Py_Initialize(); pysys_stdout.open(pysys_stdout_sink()); pysys_stdout << "Hello, Python world!\n"; } /* fin */ FIN touch project-root.jam cat > Jamfile <<FIN # Jamfile # Python library lib python2.5 ; # Build pysys_stdout example exe pysys_stdout : pysys_stdout.cpp python2.5 ; # fin. FIN ls -l
total 8 -rw-r--r-- 1 dietrich dietrich 131 2009-05-14 22:56 Jamfile -rw-r--r-- 1 dietrich dietrich 0 2009-05-14 22:56 project-root.jam -rw-r--r-- 1 dietrich dietrich 982 2009-05-14 22:56 pysys_stdout.cpp
bjam
[...]
bin/gcc-4.3.3/debug/pysys_stdout
Hello, Python world!
On Wed, 2009-05-13 at 01:11 -0700, Christopher Currie wrote:
On Mon, May 11, 2009 at 2:17 PM, Early Ehlinger <earlye@gmail.com> wrote:
Basically, you need to create a streambuf class that calls PySys_WriteStdout() inside your_streambuf_class::sync().
It's probably fairly straightforward to do this using Boost.Iostreams, by creating a model of Sink:
include <Python.h>
#include <algorithm> // min #include <iosfwd> // streamsize #include <boost/iostreams/categories.hpp> // sink_tag #include <boost/iostreams/stream.hpp> // stream #include <boost/format.hpp> // format
class pysys_stdout_sink { public: typedef char char_type; typedef boost::iostreams::sink_tag category;
std::streamsize write( const char* s, std::streamsize n ) { // PySys_WriteStdout truncates to 1000 chars static const std::streamsize MAXSIZE = 1000;
std::streamsize written = std::min( n, MAXSIZE ); PySys_WriteStdout( (boost::format("%%.%1%s") % written).str().c_str(), s );
return written; } };
boost::iostreams::stream<pysys_stdout_sink> pysys_stdout;
int main() { Py_Initialize(); pysys_stdout << "Hello, Python world!\n"; }
HTH, Christopher _______________________________________________ Boost-users mailing list Boost-users@lists.boost.org http://lists.boost.org/mailman/listinfo.cgi/boost-users
participants (3)
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Christopher Currie -
Dietrich Bollmann -
Early Ehlinger