User's Guide

Mixed-Language Input and Output

To improve performance, the XL Fortran run-time library has its own buffers and its own handling of these buffers. This means that mixed-language programs cannot freely mix I/O operations on the same file from the different languages. To maintain data integrity in such cases:

• If the file position is not important, open and explicitly close the file within the Fortran part of the program before performing any I/O operations on that file from subprograms written in another language.

• To open a file in Fortran and manipulate the open file from another language, call the flush_ procedure to save any buffer for that file, then use the getfd procedure to find the corresponding file descriptor and pass it to the non-Fortran subprogram. As an alternative to calling the flush_ procedure, you can use the buffering run-time option to disable the buffering for I/O operations. When you specify buffering=disable_preconn, XL Fortran disables the buffering for preconnected units. When you specify buffering=disable_all, XL Fortran disables the buffering for all logical units.

  Note:

  After you call flush_ to flush the buffer for a file, do not do anything to the file from the Fortran part of the program except to close it when the non-Fortran processing is finished.

• If any XL Fortran subprograms containing WRITE statements are called from a non-Fortran main program, either explicitly CLOSE the data file or use the flush_ subroutine in the XL Fortran subprograms to ensure that the buffers are flushed. Alternatively, you can use the buffering run-time option to disable buffering for I/O operations.