When writing unformatted Fortran files, IDL will continue to use 32-bit record markers. When reading FORTRAN data, IDL will attempt to recognize the presence of 64-bit record markers and switch to the appropriate format. Note: On 64-bit machines, some Fortran compilers will insert record markers that are 64-bit integers instead of the standard 32-bit integers. Use the F77_UNFORMATTED keyword if your IDL program is reading data that contain embedded longword logical record separators, or if your program is writing data that will be read by a FORTRAN program that reads unformatted sequential files. Similarly, IDL can write data using the logical record format using the F77_UNFORMATTED keyword. When a file is opened with this keyword, IDL interprets the longword counts properly and is able to read the logical records. The F77_UNFORMATTED keyword to the OPEN procedures informs IDL that the file contains unformatted data demarcated by logical record identifiers.
SCIGRAPH WITH SIMPLY FORTRAN SERIES
This mechanism allows FORTRAN-generated data files that treat data as a series of logical records to be read on platforms that use stream files.
SCIGRAPH WITH SIMPLY FORTRAN WINDOWS
In order to reconcile the FORTRAN need for logical records with these stream files, FORTRAN compilers for UNIX and Microsoft Windows provide a mechanism to add a longword integer count of the number of bytes in each logical record. In contrast, the UNIX and Microsoft Windows operating systems supported by IDL treat files as an uninterrupted stream of bytes. This system works well for operating systems like VMS, which organize files into records and can thus keep track of where logical blocks of data begin and end. To read data, the FORTRAN program asks for the next logical record from an open file the operating system is then responsible for determining how much data should be retrieved from the file. The standard FORTRAN unformatted sequential file input/output mechanism performs file input and output by reading and writing blocks of data from (or to) a file as logical records.
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