How does one generate from boost karma into C++ array? -


i see how karma can used generate container manages memory, std::string. case buffer (char[n]) has been pre-allocated?

  {     using namespace boost::spirit::karma;     {       std::string buffer;       generate(std::inserter(buffer, buffer.begin()), double_, 3.13);       std::cout << ':' << buffer << ':' << std::endl;     }     {       //////////////////////////////////////////////////////////////////////       // how make following work? there builtin output       // iterator works? #if defined(majic)       char buffer[1024];       generate(buffer, double_, 3.13);       std::cout << ':' << buffer << ':' << std::endl; #endif     }   }

i find way parse double address of existing buffer. ok assume buffer large enough case. maybe underlying question - there output iterator adapter or in karma native arrays used?

the karma iterator-based api (here) takes... output iterators.

you can create 1 array.

problem need sure buffer capacity never being insufficient:

    char buffer[1024];     char* = buffer;     karma::generate(it, karma::double_ << karma::eol, 3.13);      std::cout.write(buffer, std::distance(buffer, it));

note how cannot assume buffer nul-terminated. use generated size.

safe using array_sink:

there's more convenient, more general approach in boost iostreams safe in face of fixed-size buffers too:

    char buffer[310];     io::stream<io::array_sink> as(buffer);     boost::spirit::ostream_iterator it(as);

here's live demo demonstrates characteristics:

live on coliru

#include <boost/spirit/include/karma.hpp> #include <boost/iostreams/device/array.hpp> #include <boost/iostreams/stream.hpp>  namespace karma = boost::spirit::karma; namespace io    = boost::iostreams;  void test(std::vector<int> const& v)  {     char buffer[310];     io::stream<io::array_sink> as(buffer);     boost::spirit::ostream_iterator it(as);      using namespace karma;     if (generate(it, int_ % ", " << eol, v))     {         std::cout << "success: ";         std::cout.write(buffer, as.tellp());     } else         std::cout << "generation failed (insufficient capacity?)\n"; }  int main() {      std::cout << "should ok: \n";     std::vector<int> v(100, 1);     test(v);      std::cout << "this exceed buffer capacity: \n";     std::iota(v.begin(), v.end(), 42);     test(v); }

which prints

should ok:  success: 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1 exceed buffer capacity:  generation failed (insufficient capacity?)

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