PSS ID Number: 102698
Article Last Modified on 5/5/2001
The information in this article applies to:
- Microsoft FORTRAN Compiler for MS-DOS 5.1
This article was previously published under Q102698
SUMMARY
By calling the file I/O functions in the Windows application programming interface (API), a dynamic-link library (DLL) developed in Microsoft FORTRAN for the Microsoft Windows operating system can read from or write to binary or unformatted files. Invoking the Windows API to provide file I/O services for a FORTRAN DLL will also allow reliable access to the files from the program calling the DLL, even if the program was developed in Microsoft Visual Basic versions 2.0 and later.
MORE INFORMATION
The following FORTRAN code demonstrates file I/O on a binary or unformatted file using functions of the Windows API.
The code example below defines the data type used by the bfread and bfwrite functions as REAL*4. You can substitute another data type by changing the declaration in the interface statement.
If an application developed in Visual Basic calls a FORTRAN DLL that uses standard FORTRAN I/O statements to open and close a file, the file may not be available to the parent application. However, if the DLL opens or creates, accesses, and closes the file using functions in the Windows API, the file is available to the parent application or any other application as soon as the DLL closes the file.
The code example uses interface statements for the _hread and _hwrite functions instead of the _lread and _lwrite functions. (The latter functions can process only data items smaller than 64K but they may process these smaller items somewhat more efficiently.) The HUGE.LIB import library, created from HUGE.DEF, is required to call the huge versions of the read and write functions defined in version 3.1 of the Windows API. For more information on Windows API programming, please refer to the Windows SDK documentation.
Sample Code - FORTIO.FOR
C Open an existing file
interface to integer*2 function lopen
+ [pascal, alias:'_lopen'](filename, mode)
character*1 filename[reference]
integer*2 mode[value]
C MODE =
C 0 Read-only
C 1 Write-only
C 2 Read and write
end
C Create a file (erase the old file if one exists)
interface to integer*2 function lcreat
+ [pascal, alias:'_lcreat'](filename, mode)
character*1 filename[reference]
integer*2 mode[value]
C MODE =
C 0 Read and write
C 1 Read-only
C 2 Hidden
C 3 System
end
C Close a file (use with files opened by lcreat or lopen)
interface to integer*2 function lclose
+ [pascal, alias:'_lclose'](handle)
integer*2 handle[value]
end
C hread and hwrite can read or write a buffer larger than 64K
interface to integer*4 function hwrite
+ [pascal, alias:'_hwrite'](handle, buf, size)
character*1 buf[reference]
integer*2 handle[value]
integer*4 size[value]
end
interface to integer*4 function hread
+ [pascal, alias:'_hread'](handle, buf, size)
character*1 buf[reference]
integer*2 handle[value]
integer*4 size[value]
end
C Seek to a point in a file (used to provide direct file access)
interface to integer*4 function llseek
+ [pascal, alias:'_llseek'](handle, offset, origin)
integer*4 offset[value]
integer*2 handle[value], origin[value]
C Origin =
C 0 Offset from start of file
C 1 Offset from current position
C 2 Offset from end of file
end
C Read and write binary floating-point data
interface to integer*4 function bfwrite
+ [pascal, alias:'_hwrite'](handle, buf, size)
real*4 buf[reference](1)
integer*2 handle[value]
integer*4 size[value]
end
interface to integer*4 function bfread
+ [pascal, alias:'_hread'](handle, buf, size)
real*4 buf[reference](1)
integer*2 handle[value]
integer*4 size[value]
end
C Write ASCII and binary data
subroutine testwrite()
character*30 str
integer*2 handle, lclose, lcreat
integer*4 i, hwrite, bfwrite
real*4 x(20000) ! Note: X is 80000 bytes
handle = lcreat('testbf.out'C, 0) ! Create new file
do i= 2, 20000
x(i) = x(i - 1) + 3.1415926
end do
i = bfwrite(handle, x, 80000) ! Binary write all of X
i = lclose(handle)
handle = lcreat('test.out'C, 0) ! Create new file
! Use an internal write to format output text
write(str, '(''Test One'', F12.5)') 51.763
i = hwrite(handle, str, 20) ! then write output text
i = lclose(handle)
end
C Read binary data
subroutine readbinary()
character*24 str
integer*2 j, handle, lclose, lopen, lcreat
integer*4 i, hwrite, bfread
real*4 x(20000) ! Note: X is 80000 bytes
handle = lopen('testbf.out'C, 2) ! Open existing file
i = bfread(handle, x, 80000) ! Binary read all of X
i = lclose(handle)
handle = lcreat('testbf_o.out'C, 0) ! Create new file
do j = 1, 4
write(str, '(F16.5)') x(j) ! Convert to text
i = hwrite(handle, str, 16) ! Write formatted output
end do
write(str, '(F16.5)') x(20000)
i = hwrite(handle, str, 16)
i = lclose(handle)
end
C Randomly access a file
subroutine testseek()
character*40 str
integer*2 handle, lclose, lopen
integer*4 i, hwrite, llseek, hread
handle = lopen('test.out'C, 2)
i = llseek(handle, 4, 0) ! Position to 4 bytes from start
i = hread(handle, str, 16) ! Read 16 characters
i = llseek(handle, 7, 0) ! Position to 7 bytes from start
i = hwrite(handle, str, 16) ! Overwrite from position 7 on
i = lclose(handle)
end
FORTIO.DEF
----------
LIBRARY FORTIO
EXETYPE WINDOWS 3.1
PROTMODE
CODE PRELOAD MOVEABLE DISCARDABLE
DATA PRELOAD MOVEABLE SINGLE
HEAPSIZE 1024
EXPORTS WEP @1 RESIDENTNAME
TESTWRITE
TESTSEEK
READBINARY
TEST.FOR
--------
call testwrite
print *,"testwrite - Created 'test.out' and 'testbf.out'"
print *, 'Check them out (Hit return to continue)'
read *
call readbinary
print *, "readbinary - Created 'testbf_o.out'"
print *, 'Check it out (Hit return to continue)'
read *
call testseek ! modify 'test.out'
print *, "testseek - Modified 'test.out'"
end
HUGE.DEF
--------
LIBRARY KERNEL
EXPORTS _hread
_hwrite
FORTIO.MAK
----------
all: test.exe
test.exe: fortio.lib test.obj
link /NOD test.obj, , nul, llibfew + fortio.lib,\
c:\fortran\binb\fl.def;
test.obj: test.for
fl /c /MW test.for
fortio.lib: fortio.dll
implib fortio.lib fortio.dll
fortio.dll: fortio.obj fortio.def huge.lib
link /NOD fortio.obj, fortio.dll, nul,\
ldllfew.lib + huge.lib, fortio.def;
fortio.obj: fortio.for
fl /c /Aw /Gw fortio.for
huge.lib: huge.def
implib huge.lib huge.def
Additional query words: kbinf 5.10
Keywords: KB102698
Technology: kbAudDeveloper kbFORTRAN510DOS kbFortranSearch kbZNotKeyword3
