add error handling example

cmake/meson: add linker language parameter

meson needs link fortran

Author: scivision

README.md

@@ -25,7 +25,17 @@ https://stackoverflow.com/tags/fortran-iso-c-binding/info
 In general, CMake >= 3.14 has better link resolution than CMake 3.13.
 In general, strongly avoid the FortranCInterface of CMake and mangling function names--just use Fortran 2003 standard `bind(C)`
 
-## MacOS
+## build
+
+```sh
+cmake -B build
+
+cmake --build build
+
+ctest --test-dir build
+```
+
+### MacOS
 
 For MacOS with Apple's Clang and Homebrew GCC,
 be sure you have in ~/.zshrc like the following:
@@ -38,12 +48,7 @@ export CXXFLAGS=-I$CPLUS_INCLUDE_PATH
 export CFLAGS=$CXXFLAGS
 ```
 
-## build
-
-```sh
-cmake -B build
+## Error handling in Fortran with C/C++ main program
 
-cmake --build build
-
-ctest --test-dir build
-```
+Using Fortran statement "stop" or "error stop" with a C/C++ main program results in segmentation fault across compilers and operating systems.
+Instead, return an error code from Fortran subroutine to the C/C++ main program, and let C/C++ handle the error.

cmake/compilers.cmake

@@ -18,3 +18,8 @@ if(CMAKE_Fortran_COMPILER_ID STREQUAL GNU)
   string(APPEND CMAKE_Fortran_FLAGS " -fimplicit-none")
   add_compile_options(-Wextra -Wall)
 endif()
+
+
+if(NOT EXISTS ${PROJECT_BINARY_DIR}/.gitignore)
+  file(WRITE ${PROJECT_BINARY_DIR}/.gitignore "*")
+endif()

src/CMakeLists.txt

@@ -16,11 +16,28 @@ add_executable(fortran_call_c fortran/main.f90)
 target_link_libraries(fortran_call_c PRIVATE math_c)
 add_test(NAME Fortran_call_C COMMAND fortran_call_c)
 
+# -- C calling Fortran
+add_executable(c_fortran_error c/error_main.c)
+target_link_libraries(c_fortran_error PRIVATE error_fortran)
+# LINKER_LANGUAGE option is necessary for ifort at least
+set_target_properties(c_fortran_error PROPERTIES LINKER_LANGUAGE C)
+add_test(NAME C_Fortran_error COMMAND c_fortran_error)
+
 # -- C++ calling Fortran
 add_executable(cxx_call_fortran cxx/main.cxx)
 target_link_libraries(cxx_call_fortran PRIVATE math_fortran)
-add_test(NAME C++_call_Fortran COMMAND cxx_call_fortran)
+add_test(NAME C++_Fortran_math COMMAND cxx_call_fortran)
+
+add_executable(cxx_fortran_error cxx/error_main.cxx)
+target_link_libraries(cxx_fortran_error PRIVATE error_fortran)
+# LINKER_LANGUAGE option is necessary for ifort at least
+set_target_properties(cxx_fortran_error PROPERTIES LINKER_LANGUAGE CXX)
+add_test(NAME C++_Fortran_error COMMAND cxx_fortran_error)
+
+# -- test wrapup
+
+set_tests_properties(C++_Fortran_error C_Fortran_error PROPERTIES WILL_FAIL TRUE)
 
-set_tests_properties(C++_call_Fortran Fortran_call_C Fortran_call_C++ PROPERTIES
+set_tests_properties(C++_Fortran_math C++_Fortran_error Fortran_call_C Fortran_call_C++ PROPERTIES
 TIMEOUT 5
 )

src/c/error_main.c

@@ -0,0 +1,9 @@
+// Example of Fortran erroring with C main
+
+extern void error_fortran(int*);
+
+int main(void) {
+  int code = 42;
+  error_fortran(&code);
+  return 0;
+}

src/cxx/error_main.cxx

@@ -0,0 +1,9 @@
+// Example of Fortran erroring with C++ main
+
+extern "C" void error_fortran(int*);
+
+int main() {
+  int code = 42;
+  error_fortran(&code);
+  return 0;
+}

src/fortran/CMakeLists.txt

@@ -1 +1,3 @@
 add_library(math_fortran OBJECT math.f90)
+
+add_library(error_fortran OBJECT error.f90)

src/fortran/error.f90

@@ -0,0 +1,16 @@
+module utils
+
+use, intrinsic :: iso_c_binding, only : c_int
+implicit none (type, external)
+
+contains
+
+subroutine error_fortran(value) bind(C)
+
+  integer(c_int), intent(in) :: value
+
+  error stop value
+
+end subroutine error_fortran
+
+end module utils

src/fortran/meson.build

@@ -1 +1,3 @@
 math_fortran = library('math_fortran', 'math.f90')
+
+error_fortran = library('error_fortran', 'error.f90')

src/meson.build

@@ -8,7 +8,8 @@ subdir('fortran')
 fortran_call_cxx = executable('fortran_call_cxx',
   sources: files('fortran/main.f90'),
   link_with: math_cxx,
-  link_language: 'fortran')
+  link_language: 'fortran'
+)
 test('Fortran call C++', fortran_call_cxx, timeout: 5)
 
 # -- Fortran calling C
@@ -19,8 +20,28 @@ fortran_call_c = executable('fortran_call_c',
 )
 test('Fortran call C', fortran_call_c,  timeout: 5)
 
+# -- C calling Fortran
+c_fortran_error = executable('c_fortran_error',
+  sources: files('c/error_main.c'),
+  link_with: error_fortran,
+  link_language: 'fortran'
+)
+test('C Fortran error', c_fortran_error,
+  timeout: 5,
+  should_fail: true)
+
 # -- C++ calling Fortran
 cxx_call_fortran = executable('cxx_call_fortran',
   sources: files('cxx/main.cxx'),
-  link_with: math_fortran)
-test('C++ calling Fortran', cxx_call_fortran, timeout: 10)
+  link_with: math_fortran
+)
+test('C++ call Fortran', cxx_call_fortran, timeout: 5)
+
+cxx_fortran_error = executable('cxx_fortran_error',
+  sources: files('cxx/error_main.cxx'),
+  link_with: error_fortran,
+  link_language: 'fortran'
+)
+test('C++ Fortran error', cxx_fortran_error,
+  timeout: 5,
+  should_fail: true)