Re: [Boost-users] (Boost.Python) How to print from C++ to the same stream as Python's 'print' does?

14 May 2009

      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;
	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 <

#include <algorithm>                       // min
#include <iosfwd>                          // streamsize
#include   // sink_tag
#include       // stream
#include                 // 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;

int main()
{
    Py_Initialize();
    pysys_stdout.open(pysys_stdout_sink()); 
    pysys_stdout << "Hello, Python world!\n";
}

/* fin */
FIN

touch project-root.jam

cat > Jamfile <
...
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  wrote:
...
Basically, you need to create a streambuf class that calls
PySys_WriteStdout() inside your_streambuf_class::sync().
...
http://lists.boost.org/mailman/listinfo.cgi/boost-users
It's probably fairly straightforward to do this using Boost.Iostreams,
by creating a model of Sink:
include 
#include <algorithm>                       // min
#include <iosfwd>                          // streamsize
#include   // sink_tag
#include       // stream
#include                 // 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;
int main()
{
    Py_Initialize();
    pysys_stdout << "Hello, Python world!\n";
}
HTH,
Christopher
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Re: [Boost-users] (Boost.Python) How to print from C++ to the same stream as Python's 'print' does?

Dietrich Bollmann