Environment variables of significance to Fortran execution

A few environment variables are queried by the Fortran runtime support library.

The following environment variables can affect the behavior of Fortran programs during execution.


Set DEFAULT_UTF8 to cause formatted external input to assume UTF-8 encoding on input and use UTF-8 encoding on formatted external output.


Determines data conversions applied to unformatted I/O.

  • NATIVE: no conversions (default)

  • LITTLE_ENDIAN: assume input is little-endian; emit little-endian output

  • BIG_ENDIAN: assume input is big-endian; emit big-endian output

  • SWAP: reverse endianness (always convert)


Fortran requires that a pointer that appears in a DEALLOCATE statement must have been allocated in an ALLOCATE statement with the same declared type. The runtime support library validates this requirement by checking the size of the allocated data, and will fail with an error message if the deallocated pointer is not valid. Set FORT_CHECK_POINTER_DEALLOCATION=0 to disable this check.


Set to an integer value to specify the record length for list-directed and NAMELIST output. The default is 72.


Set NO_STOP_MESSAGE=1 to disable the extra information about IEEE floating-point exception flags that the Fortran language standard requires for STOP and ERROR STOP statements.