I'm getting this unhandled exception when I exit my program:
Unhandled exception at 0x102fe274 (msvcr100d.dll) in Parameters.exe: 0xC0000005: Access violation reading location 0x00000005.
The debugger stops in a module called crtdll.c on this line:
onexitbegin_new = (_PVFV *) DecodePointer(__onexitbegin);
The top line on the call stack reads:
msvcr100d.dll!__clean_type_info_names_internal(__type_info_node * p_type_info_root_node=0x04a6506c) Line 359 + 0x3 bytes C++
The program then remains in memory until I close down the IDE.
I'm more used to developing with managed languages so I expect I'm doing something wrong with my code maintenance. The code itself reads a memory mapped file and assoiciates it with pointers:
SUBROUTINE READ_MMF ()
USE IFWIN
USE, INTRINSIC :: iso_c_binding
USE, INTRINSIC :: iso_fortran_env
INTEGER(HANDLE) file_mapping_handle
INTEGER(LPVOID) memory_location
TYPE(C_PTR) memory_location_cptr
INTEGER memory_size
INTEGER (HANDLE) file_map
CHARACTER(5) :: map_name
TYPE(C_PTR) :: cdata
integer :: n = 3
integer(4), POINTER :: A, C
real(8), POINTER :: B
TYPE STRUCT
integer(4) :: A
real(8) :: B
integer(4) :: C
END TYPE STRUCT
TYPE(STRUCT), pointer :: STRUCT_PTR
memory_size = 100000
map_name = 'myMMF'
file_map = CreateFileMapping(INVALID_HANDLE_VALUE,
+ NULL,
+ PAGE_READWRITE,
+ 0,
+ memory_size,
+ map_name // C_NULL_CHAR )
memory_location = MapViewOfFile(file_map,
+IOR(FILE_MAP_WRITE, FILE_MAP_READ),
+ 0, 0, 0 )
cdata = TRANSFER(memory_location, memory_location_cptr)
call c_f_pointer(cdata, STRUCT_PTR, [n])
A => STRUCT_PTR%A
B => STRUCT_PTR%B
C => STRUCT_PTR%C
RETURN
END
Am I supposed to deallocate the c-pointers when I'm finished with them? I looked into that but can't see how I do it in Fortran...
Thanks for any help!
The nature of the access violation (during runtime library cleanup) suggests that your program is corrupting memory in some way. There are a number of programming errors that can lead to that - and the error or errors responsible could be anywhere in your program. The usual "compile and run with all diagnostic and debugging options enabled" approach may help identify these.
That said, there is a programming error in the code example shown. The C_F_POINTER procedure from the ISO_C_BINDING intrinsic module can operate on either scalar or array Fortran pointers (the second argument). If the Fortran pointer is a scalar then the third "shape" argument must not be present (it must be present if the Fortran pointer is an array).
Your code breaks this requirement - the Fortran pointer STRUCT_PTR in your code is a scalar, but yet you provide the third shape argument (as [n]). It is quite plausible that this error will result in memory corruption - typically the implementation of C_F_POINTER would try and populate a descriptor in memory for the Fortran pointer, and the descriptor for a pointer to an array may be very different from a pointer to a scalar.
Subsequent references to STRUCT_PTR may further the corruption.
While it is not required by the standard to diagnose this situation, I am a little surprised that the compiler does not issue a diagnostic (assuming you example code is what you actually are compiling). If you reported this to your compiler's vendor (Intel, presumably given IFWIN etc) I suspect they would regard it as a deficiency in their compiler.
To release the memory associated with the file mapping you use the UnmapViewOfFile and CloseHandle API's. To use these you should "store" (your program needs to remember in some way) the base address (memory_location, which can also be obtained by calling C_LOC on STRUCT_PTR once the problem above is fixed) returned by MapViewOfFile, and the handle to the mapping (file_map) returned by CreateFileMapping; respectively.