iso_fortran_binding string

Author: scivision

test/iso_fortran_binding/CMakeLists.txt

@@ -32,6 +32,14 @@ if(HAVE_C_CHAR_PTR)
   add_test(NAME CFI_establish_string COMMAND cfi_establish_string)
 
   if(HAVE_CFI_CDESC)
+    add_executable(string_inout_c string_inout.c string_inout.f90)
+    set_property(TARGET string_inout_c PROPERTY LINKER_LANGUAGE Fortran)
+    add_test(NAME StringInOutC COMMAND string_inout_c)
+
+    add_executable(string_inout_cpp string_inout.cpp string_inout.f90)
+    set_property(TARGET string_inout_cpp PROPERTY LINKER_LANGUAGE Fortran)
+    add_test(NAME StringInOutCPP COMMAND string_inout_cpp)
+
     add_executable(string_array string_array.cpp string_array.f90)
     set_property(TARGET string_array PROPERTY LINKER_LANGUAGE CXX)
     target_compile_options(string_array PRIVATE "$<$<COMPILE_LANG_AND_ID:Fortran,GNU>:-Wno-uninitialized>")

test/iso_fortran_binding/c_string.c

@@ -1,6 +1,6 @@
 // https://fortran-lang.discourse.group/t/experiment-dealing-with-a-pointer-to-a-string-from-c/930/3
 #include <string.h>
-#include "ISO_Fortran_binding.h"
+#include <ISO_Fortran_binding.h>
 
 static char *str = "Hello";
 

test/iso_fortran_binding/string_array.cpp

@@ -5,7 +5,7 @@
 #include <iostream>
 #include <cstdlib>
 
-#include "ISO_Fortran_binding.h"
+#include <ISO_Fortran_binding.h>
 
 extern "C" {
    // Prototype for the Fortran procedures

test/iso_fortran_binding/string_inout.c

@@ -0,0 +1,21 @@
+#include <string.h>
+
+#include <ISO_Fortran_binding.h>
+
+void process_strings_cfi(const CFI_cdesc_t *in_desc, CFI_cdesc_t *out_desc) {
+    // 1. Get exact lengths directly from the Fortran descriptor
+    size_t in_len  = in_desc->elem_len;
+    size_t out_len = out_desc->elem_len;
+
+    // 2. Direct pointer access to Fortran's memory
+    char *in_ptr  = (char*)(in_desc->base_addr);
+    char *out_ptr = (char*)(out_desc->base_addr);
+
+    // Note: Fortran strings are NOT null-terminated!
+    // You must use bounded memory operations:
+    // printf("C received exact characters: %.*s\n", (int)in_len, in_ptr);
+
+    // Write safely back to Fortran's allocated memory space
+    memset(out_ptr, ' ', out_len); // Clear with Fortran space-padding
+    strncpy(out_ptr, "Success", out_len < 7 ? out_len : 7);
+}

test/iso_fortran_binding/string_inout.cpp

@@ -0,0 +1,27 @@
+#include <algorithm> // for std::min
+#include <string>
+
+#include <ISO_Fortran_binding.h>
+
+extern "C" {
+    void process_strings_cfi(const CFI_cdesc_t *, CFI_cdesc_t *);
+}
+
+
+void process_strings_cfi(const CFI_cdesc_t *in_desc, CFI_cdesc_t *out_desc) {
+    const std::string::size_type in_len = in_desc->elem_len;
+    const std::string::size_type out_len = out_desc->elem_len;
+
+    const char *in_ptr = static_cast<const char *>(in_desc->base_addr);
+    char *out_ptr = static_cast<char *>(out_desc->base_addr);
+
+    // Fortran character data is fixed-width and not null-terminated.
+    const std::string in_value(in_ptr, in_len);
+    (void)in_value;
+    const std::string out_value("Success");
+
+    // Copy into Fortran buffer using space-padding semantics.
+    std::string fortran_out(out_len, ' ');
+    fortran_out.replace(0, std::min(out_len, out_value.size()), out_value, 0, std::min(out_len, out_value.size()));
+    fortran_out.copy(out_ptr, out_len);
+}

test/iso_fortran_binding/string_inout.f90

@@ -0,0 +1,21 @@
+program string_inout_cpp
+
+implicit none
+
+interface
+subroutine process_strings_direct(in_str, out_str) bind(C, name="process_strings_cfi")
+character(len=*), intent(in)  :: in_str
+character(len=*), intent(out) :: out_str
+end subroutine process_strings_direct
+end interface
+
+
+character(len=20) :: input_str  = "Hello from Fortran!"
+character(len=20) :: output_str
+
+call process_strings_direct(input_str, output_str)
+
+print *, "Fortran sent: ", trim(input_str)
+print *, "Fortran received: ", trim(output_str)
+
+end program

test/iso_fortran_binding/string_view.cpp

@@ -3,7 +3,7 @@
 #include <string_view>
 #include <iostream>
 
-#include "ISO_Fortran_binding.h"
+#include <ISO_Fortran_binding.h>
 
 extern "C" {
    void echo_c( const CFI_cdesc_t* Fstr )