add c_f_pointer example

Author: scivision

src/cxx/CMakeLists.txt

@@ -19,6 +19,10 @@ add_executable(cxx_fortran_vector vector_main.cxx)
 target_link_libraries(cxx_fortran_vector PRIVATE vector_fortran)
 add_test(NAME C++_Fortran_vector COMMAND cxx_fortran_vector)
 
+add_executable(cxx_fortran_pointer pointer_main.cxx)
+target_link_libraries(cxx_fortran_pointer PRIVATE pointer_fortran)
+add_test(NAME C++_Fortran_pointer COMMAND cxx_fortran_pointer)
+
 add_executable(cxx_fortran_error error_main.cxx)
 target_link_libraries(cxx_fortran_error PRIVATE error_fortran)
 # LINKER_LANGUAGE option is necessary for ifort at least

src/cxx/pointer_main.cxx

@@ -0,0 +1,23 @@
+#include <iostream>
+#include <vector>
+
+extern "C" void point23(float [], float [], size_t*);
+
+
+int main()
+{
+
+  std::vector<float> a = {0, 1, 2};
+  auto N = a.size();
+  std::vector<float> b(2);
+
+  point23(&a.front(), &b.front(), &N);
+
+  if (b[0] != a[1] || b[1] != a[2]){
+    std::cerr << "value " <<  b[0] << "!=" << a[1] << " or " << b[1] << "!=" << a[2] << std::endl;
+    return EXIT_FAILURE;
+  }
+
+  std::cout << "OK: C++ to Fortran pointer" << std::endl;
+  return EXIT_SUCCESS;
+}

src/fortran/CMakeLists.txt

@@ -2,6 +2,8 @@ add_library(vector_fortran OBJECT vector_lib.f90)
 
 add_library(error_fortran OBJECT error_lib.f90)
 
+add_library(pointer_fortran OBJECT pointer_lib.f90)
+
 add_library(struct_fortran OBJECT struct_lib.f90)
 
 add_library(submodule_fortran OBJECT module.f90 submodule.f90)

src/fortran/meson.build

@@ -2,9 +2,9 @@ vector_fortran = library('vector_fortran', 'vector_lib.f90')
 
 error_fortran = library('error_fortran', 'error_lib.f90')
 
-struct_fortran = library('struct_fortran',
-sources: 'struct_lib.f90'
-)
+pointer_fortran = library('pointer_fortran', 'pointer_lib.f90')
+
+struct_fortran = library('struct_fortran', 'struct_lib.f90')
 
 submodule_fortran = library('submodule',
 sources: ['module.f90', 'submodule.f90']

src/fortran/pointer_lib.f90

@@ -0,0 +1,28 @@
+!! This example is overly complicated way to do this task,
+!! but it's just to show how c_f_pointer() can work, although it would normally be for more advanced
+!! use cases as this task could be done like vector_lib.f90.
+module p
+
+use, intrinsic :: iso_c_binding, only : C_FLOAT, C_SIZE_T, C_PTR, c_f_pointer, c_associated
+implicit none (type, external)
+
+contains
+
+subroutine point23(p1, b, N) bind(C)
+
+type(C_PTR), value, intent(in) :: p1
+real(C_FLOAT), intent(out) :: b(2)
+integer(C_SIZE_T), intent(in) :: N
+
+real(C_FLOAT), pointer :: D(:)
+
+call c_f_pointer(p1, D, [N])
+
+if(.not. C_associated(p1)) error stop "input pointer not C associated"
+if(.not. associated(D)) error stop "data array pointer not associated"
+
+B = D(2:3)
+
+end subroutine point23
+
+end module p

src/fortran/vector_main.f90

@@ -1,8 +1,4 @@
-program call_c
-!! Demonstrate Fortran calling C or C++.
-!!
-!! Normally BIND(C) should be used after the function name in the interface block,
-!! rather than postpending underscore(s).
+program vector
 
 use, intrinsic :: iso_c_binding, only: c_int
 implicit none (type, external)

src/meson.build

@@ -68,3 +68,11 @@ link_language: 'fortran'
 test('C++ Fortran struct', cxx_fortran_struct,
 timeout: 5
 )
+
+cxx_fortran_pointer = executable('cxx_fortran_pointer',
+sources: files('cxx/pointer_main.cxx'),
+link_with: pointer_fortran
+)
+test('C++ Fortran pointer', cxx_fortran_pointer,
+timeout: 5
+)