9.5.4. Matching Data Representations


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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'' , 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 ).
  • For any given data item, the programs participating in the data accesses use compatible predefined types to write and read the data item.

User-defined data representations may be used to provide an implementation compatiblity with another implementation's ``native'' or ``internal'' representation.


[] Advice to users.

Section 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.)


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