How to send by socket C++ compatible struct from Java? -

suppose there written, unchangeable host program, receives such c++ struct socket:

#pragma pack(push, 2) struct data {   double x;   double y;   double z;   long framenumber; }; #pragma pack(pop)  

platform: c++ / 32-bit windows application compiled in visual studio 2008

how send such data java socket? have attemted fill bytebuffer putdouble(), , putlong(), putint() assuming long 32-bit, cannot produce valid values.

i have generated , sended data randomly, , structure-level bytes assignment looks fine(i can randomize 1 value, example x), cannot produce exact value (propably different double representation?), random stuff sending math.random() * double.max_value;

can use google protocol buffers on 1 side (client producing data) solve problem?

remember, cannot change server (receiving) side

i know can move sending data c++ , use jni, i'm searching simpler solution.

i see @ least 2 possible problems here:

• double representation @ byte-level (like 01234567 , 76543210 on other side)
• bits representation in 1 byte (like 00000001 , 1000000 on other side)

what things in java in c++?

in several hours provide exact sample data "byte-hacking" (exact java value before send , value of received double in c++)

about server bad-design answering

i know such implemented , unchangeable server bad software, environment in problem inject data small old application @ "hobbistic-level"

java representation

maybe bits-level c++ expert:

long.tobinarystring( double.doubletorawlongbits( (double) 0 ) ); // 000000000000000000000000000000000000000000000000000000000000000  long.tobinarystring( double.doubletorawlongbits( 1 ) ); // 011111111110000000000000000000000000000000000000000000000000000  long.tobinarystring( double.doubletorawlongbits( 1.1 ) ); // 011111111110001100110011001100110011001100110011001100110011010  long.tobinarystring( double.doubletorawlongbits( 1024 ) ); // 100000010010000000000000000000000000000000000000000000000000000  long.tobinarystring( double.doubletorawlongbits( 1024.1024 ) ); // 100000010010000000000000110100011011011100010111010110001110001  long.tobinarystring( double.doubletorawlongbits( double.max_value ) ); // 111111111101111111111111111111111111111111111111111111111111111 

suppose there written, unchangeable host program, receives such c++ struct socket

then have major problem unknown person has kindly left legacy. have produce java code conform specific c++ compiler's conception of wire format of specific struct, depends on:

• the hardware
• the compiler vendor
• the compiler version
• the compilation options
• the surrounding #pragmas
• ...

i strongly suggest you take opportunity fix whole megillah , define proper wire format transaction.

once you've done can emulate enough facilities of dataoutputstream, or if problem worse , endian-ness involved, nio plus bytebuffer.