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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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MPI-2.0 of July 18, 1997
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