[Boost-users] [Interprocess] How to make a clean print using a managed file mapping?

Subject: [Boost-users] [Interprocess] How to make a clean print using a managed file mapping?
From: Alexander Maslowski (alexmas_at_[hidden])
Date: 2010-02-05 20:27:31

Interprocess newbie question.

I’m trying to use interprocess to print a data file to possibly
improve the speed of my code.
I’ve attached a code sample to the bottom.  The code compiles with msn
cl compiler, but segfaults with gcc (4.3.2).

Two questions:
Is it possible to produce a file that is not junked up with binary at
the beginning and end?
Any ideas why it seg-faults with gcc?

Thanks in advance.

--Alex

#include <boost/interprocess/managed_mapped_file.hpp>
#include <boost/interprocess/streams/bufferstream.hpp>

#include <boost/filesystem/path.hpp>
#include <boost/filesystem/operations.hpp>

#include <exception>
#include <iostream>
#include <vector>

int main( int /*argc*/, char** /*argv*/ )
{
       using namespace std;
       using namespace boost;

       //Initialize the data to be printed
       size_t dataSetSize = 10;
       vector<double> coordinate(dataSetSize);
       vector<double> magnitude (dataSetSize);

       for( size_t i = 0; i < dataSetSize; ++i){
               coordinate[i] = static_cast<double>(i);
               magnitude [i] = static_cast<double>(2*i) +
static_cast<double>(2*i)/1e10;
       }

       vector<string> banner(2);
       banner[0]="this is my data file banner\n";
       banner[1]="file end";
       string fileName("fileMapperTest.out");

       try{
               using namespace filesystem;
               using namespace interprocess;

               //Remove the file if it already exists
               path fileNamePath(fileName);
               if( exists(fileNamePath) ) remove(fileNamePath);

               size_t dataWidth = 20;
               size_t bufferSize =
banner[0].size()+2*dataSetSize*(dataWidth+3)+banner[1].size();

               //map the file
               managed_mapped_file tstFileMap( create_only, fileName.c_str(),
                       2*bufferSize);
               cout << "file was mapped" << endl;

               //create a buffer
               char *aString = tstFileMap.construct<char>("aString")
                       [bufferSize]();
               cout << "the buffer was constructed" << endl;

               //stream into the buffer
               bufferstream testFileBuff(aString, bufferSize, ios_base::out);
               testFileBuff.precision(dataWidth-5);
               cout.precision(dataWidth-5);
               cout << "the buffer stream was constructed" << endl;

               //Start printing
               testFileBuff << banner[0] << "\n";

               for( size_t i = 0; i < dataSetSize; ++i){
                       testFileBuff << coordinate[i] << " "
                                                << magnitude [i] << "\n";
                       cout << coordinate[i] << " " << magnitude [i] << "\n";
               }

               testFileBuff << banner[1] << endl;

               tstFileMap.destroy_ptr(aString);

       }

       catch(interprocess::interprocess_exception& e)
       {
               cout << "An interprocess exception was thrown ..." << endl;
               cout << e.what() << endl;
       }

       catch(...)
       {
               cout << "An unknown exception was thrown ..." << endl;
       }

       return 0;
}

My file output:
[binary junk]...
0 0
1 2.0000000002
2 4.0000000004
3 6.0000000006
4 8.0000000008
5 10.000000001
6 12.0000000012
7 14.0000000014
8 16.0000000016
9 18.0000000018
file end
[more binary junk]