# Use a Third-Party Compiler as a Host Compiler for DPC++ Code

This content describes the steps needed to use an external host compiler (G++*) along with the Intel® oneAPI DPC++/C++ Compiler.

In this example, you will use a host compiler to generate the host objects and perform the final link. The host compiler needs to know where to find the required headers and libraries. Follow the example instructions to build a Data Parallel C++ (DPC++) program using a G++ Compiler (`g++`) for host code and an Intel® oneAPI DPC++/C++ Compiler (`dpcpp`) for DPC++ code.

## For Linux*

This example includes the following:

- `a.cpp`: DPC++ code
- `b.cpp`: DPC++ code
- `main.cpp`: C++ code

1. Follow the Get Started with the Intel® oneAPI Base Toolkit for Linux* guide to set up the build environment:

   ### Note

   The build environment requires GCC* version 5.1 or above to be installed and accessible.

       source /opt/intel/oneapi/setvars.sh

2. Set up the headers and library locations:

       export LIBDIR=<Location of libsycl.so>
       export INCLUDEDIR=<Location of SYCL headers>

3. Build the objects for your device:

       dpcpp -c a.cpp -fPIC -o a.o
       dpcpp -c b.cpp -fPIC -o b.o

4. Create the integration header files (used by the host compiler):

       dpcpp -fsycl-device-only -Xclang -fsycl-int-header=a_host.h a.cpp
       dpcpp -fsycl-device-only -Xclang -fsycl-int-header=b_host.h b.cpp

5. Create the host objects:

       g++ -std=c++17 -c a.cpp -o a_host.o -include a_host.h -fPIC -I$INCLUDEDIR
       g++ -std=c++17 -c b.cpp -o b_host.o -include b_host.h -fPIC -I$INCLUDEDIR

6. Compile other C++ code (or non-DPC++ code) using G++:

       g++ -std=c++17 main.cpp -c -fPIC -I$INCLUDEDIR

7. Create a device object:

       dpcpp -fPIC -fsycl -fsycl-link a.o b.o -o device.o

8. Create an archive `libuser.a` that contains the necessary host and device objects:

   ### Note

   This step is optional.

       ar -rcs libuser.a a_host.o b_host.o device.o

9. Perform the final link to create a `final.exe` executable:

       g++ main.o a_host.o b_host.o device.o -L$LIBDIR -lOpenCL -lsycl -o finalexe.exe

10. Build the `final.exe` with an archive:

    ### Note

    This step is optional.

        g++ main.o -Wl,--whole-archive libuser.a -Wl,--no-whole-archive -L$LIBDIR -lOpenCL -lsycl -o finalexe.exe

## For Windows*

Windows is not supported in this release.

## Options

The compiler has two options that let you use an external compiler to perform host side compilation. The options are:

- `fsycl-host-compiler`: Tells the compiler to use the specified compiler for host compilation of the performed offloading compilation.
- `fsycl-host-compiler-options`: Passes options to the compiler specified by the option `fsycl-host-compiler`.

Parent topic: Compilation

## See Also

fsycl-host-compiler
fsycl-host-compiler-options