a55e30b12c
The ISO Fortran standards don't say whether a WRITE to a formatted stream unit should truncate the unit if there has been any repositioning (via POS= control list specifiers) to an earlier point in the stream. But units with sequential records do truncate on writes after BACKSPACE and REWIND statements, and many compilers (including this one) truncate stream units too. Since some compilers don't truncate streams, this patch adds an environment variable FORT_TRUNCATE_STREAM that can be set to 0 to disable truncation and ease porting to flang-new of codes that depend on that behavior. Fixes https://github.com/llvm/llvm-project/issues/167569.
2.2 KiB
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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.
DEFAULT_UTF8=1
Set DEFAULT_UTF8 to cause formatted external input to assume UTF-8
encoding on input and use UTF-8 encoding on formatted external output.
FORT_CONVERT
Determines data conversions applied to unformatted I/O.
NATIVE: no conversions (default)LITTLE_ENDIAN: assume input is little-endian; emit little-endian outputBIG_ENDIAN: assume input is big-endian; emit big-endian outputSWAP: reverse endianness (always convert)
FORT_CHECK_POINTER_DEALLOCATION
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.
FORT_FMT_RECL
Set to an integer value to specify the record length for list-directed
and NAMELIST output.
The default is 72.
NO_STOP_MESSAGE
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.
FORT_TRUNCATE_STREAM
Set FORT_TRUNCATE_STREAM=1 to make output to a formatted unit
with ACCESS="STREAM" truncate the file when the unit has been
repositioned via POS= to an earlier point in the file.
This behavior is analogous to the implicit writing of an ENDFILE record
when output takes place to a sequential unit after
executing a BACKSPACE or REWIND statement.
Truncation of a stream-access unit is common to several other
compilers, but it is not mentioned in the standard.