269. Matching Data Representations

It is the user's responsibility to ensure that the data representation used to read data from a file is compatible with the data representation that was used to write that data to the file.

In general, using the same data representation name when writing and reading a file does not guarantee that the representation is compatible. Similarly, using different representation names on two different implementations may yield compatible representations.

Compatibility can be obtained when ``external32'' representation is used, although precision may be lost and the performance may be less than when ``native'' representation is used. Compatibility is guaranteed using "external32" provided at least one of the following conditions is met.

• The data access routines directly use types enumerated in Section External Data Representation: ``external32'' , page External Data Representation: ``external32'' , that are supported by all implementations participating in the I/O. The predefined type used to write a data item must also be used to read a data item.
• In the case of Fortran 90 programs, the programs participating in the data accesses obtain compatible datatypes using MPI routines that specify precision and/or range (Section Additional Support for Fortran Numeric Intrinsic Types , page Additional Support for Fortran Numeric Intrinsic Types ).
• For any given data item, the programs participating in the data accesses use compatible predefined types to write and read the data item.

Advice to users.

Section Additional Support for Fortran Numeric Intrinsic Types , page Additional Support for Fortran Numeric Intrinsic Types , defines routines that support the use of matching datatypes in heterogeneous environments and contains examples illustrating their use. ( End of advice to users.)