C++ interface with Cx51 simulator

"Is it possible to connect an external C++ code (which does not run on 8051) with a 8051 C code ?"

You cannot connect code.

You can, of course, connect two processors via an interface of your choice; then define a suitable protocol; then write suitable software for each processor to perform the required actions.

This is, after all, how a debugger works!

If your 8051 has on-chip debug hardware and a JTAG interfase (eg, Triscend & Cygnal), you don't even need any software on the 8051.

"Is it possible to access the memory space of a 8051 C code, running on the simulator, from an external program?"

Keil provide various interfaces to uVision - I think AGSI is the one you want?
There's also a DDE interface.

There's Application Notes describing both.

"Is it possible to connect an external C++ code (which does not run on 8051) with a 8051 C code ?"

You cannot connect code.

You can, of course, connect two processors via an interface of your choice; then define a suitable protocol; then write suitable software for each processor to perform the required actions.

This is, after all, how a debugger works!

If your 8051 has on-chip debug hardware and a JTAG interfase (eg, Triscend & Cygnal), you don't even need any software on the 8051.

"Is it possible to access the memory space of a 8051 C code, running on the simulator, from an external program?"

Keil provide various interfaces to uVision - I think AGSI is the one you want?
There's also a DDE interface.

There's Application Notes describing both.