C++ and Postgresql without libpq++ and SQLAPI++

Question

How can I make an interface between C++ and Postgresql without using libpq++ or SQLAPI++ because I tried to install these two libraries but I wasn't able (no tutorials for windows). I know that Postgis and Pgrouting use C++ .. Maybe they use another library to interface with Postgresql ...

Thank you :D

Answer 1

Useful documentation:

• https://www.postgresql.org/docs/current/static/spi.html
• https://www.postgresql.org/docs/current/static/xfunc-c.html
  • Use the: 35.9.4. Version 1 Calling Conventions

For a function foo that is to be coded with c++ and is going to return sets I have the following files:

• foo.c
• foo_driver.h
• foo_driver.cpp

foo.c

follows the "35.9.9. Returning Sets (A complete example of a simple SRF returning a composite type looks like)" except that we call a static function that is going to do some stuff (mostly read more data) before calling the actual c++ function.

  static process ( char* a, bool b, bool c, mystruct* result_tuples, int result_count) {

    <maybe some checking or conversions here of a, b, & c>
    call_cpp_function( a1, b1, c1, result_tuples, result_count )

    }

    PG_FUNCTION_INFO_V1(foo);
    Datum
    foo(PG_FUNCTION_ARGS)    {
      ...
      process(
                pgr_text2char(PG_GETARG_TEXT_P(0)),
                PG_GETARG_BOOL(1),
                PG_GETARG_BOOL(2),
                &result_tuples,
                &result_count);
      ...
      } // end of first call
      ...
      if (call_cntr < max_calls) {
      ...
      else {
        free(result_tuples);
        SRF_RETURN_DONE(funcctx);
      }
    };

foo_driver Has the definition of the C++ function that is going to be used on the C code and on the C++ code

#ifdef __cplusplus
extern "C" {
#endif

void  call_cpp_function( <parameters > );


#ifdef __cplusplus
}
#endif

foo_driver.cpp

has the actual cpp code of the function "call_cpp_function" non of the postgres files are to be included here, and of course you can include more c++ files here. Particular rules:

• don't forget the try/catch or you can crash the server
• as soon as possible convert the C arrays to C++ containers
• don't use pointers on the C++ code except
  • when creating the resulting C array (remember my example returns a set)
• and dont forget the "free" statement after the last call is done

for example

#include < vector >
#include < deque >
#include "myclass.h"
void  call_cpp_function( <parameters > ) {
  try {
   <process>
   // use malloc to prepare the C array


  } catch( .. ) {
  // do cleanup
  }
}

Note: things not covered in this answer: compiling, linking, adding as an extension.