# 7.3. Error codes and classes

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The error codes returned by MPI are left entirely to the implementation (with the exception of MPI_SUCCESS). This is done to allow an implementation to provide as much information as possible in the error code (for use with MPI_ERROR_STRING).

To make it possible for an application to interpret an error code, the routine MPI_ERROR_CLASS converts any error code into one of a small set of standard error codes, called error classes. Valid error classes include

The error classes are a subset of the error codes: an MPI function may return an error class number; and the function MPI_ERROR_STRING can be used to compute the error string associated with an error class.

The error codes satisfy,

[] Rationale.

The difference between MPI_ERR_UNKNOWN and MPI_ERR_OTHER is that MPI_ERROR_STRING can return useful information about MPI_ERR_OTHER.

Note that MPI_SUCCESS = 0 is necessary to be consistent with C practice; the separation of error classes and error codes allows us to define the error classes this way. Having a known LASTCODE is often a nice sanity check as well. ( End of rationale.)
MPI_ERROR_CLASS( errorcode, errorclass )
[ IN errorcode] Error code returned by an MPI routine
[ OUT errorclass] Error class associated with errorcode

`int MPI_Error_class(int errorcode, int *errorclass)
`

`MPI_ERROR_CLASS(ERRORCODE, ERRORCLASS, IERROR)
INTEGER ERRORCODE, ERRORCLASS, IERROR
`

The function MPI_ERROR_CLASS maps each standard error code (error class) onto itself.

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