5.2 Obsolete Extensions

The following extensions were common in the Fortran 77 era, and are still in frequent use (though they have been superseded and are thus unnecessary). Warning messages (marked ‘Extension:’) are produced for each occurrence of any extension; these particular ones may be suppressed with the -w=x77 option.

5.2.1 Byte Sizes

The byte length may also be overridden in the type declaration, similar to overriding the character length. For example,

    REAL X*4, Y*(8)

5.2.2 TAB Format

1. an initial TAB followed by a digit is expanded to 5 spaces (putting the digit in the continuation column),
2. an initial TAB followed by any other character is expanded to 6 spaces (putting the character after the TAB in column 7, making the line the initial line of a statement), and
3. other TAB characters are treated as single blanks except in character context where they remain TABs (but they are still treated as taking one column for the purposes of line length).

5.2.3 Hollerith Constants

Hollerith i/o (i.e., use of the A edit descriptor with non-CHARACTER data) is only enabled if the using subprogram was compiled with the -hollerith_io or -dusty option.

5.2.4 D (debug) lines in Fixed Source Form

For example, in

      SUBROUTINE TEST(N)
      INTEGER N
D     PRINT *,'TESTING N'
      ...

Note that if the initial line of a statement is a D line, any continuation lines it may have must also be D lines. Similarly, if the initial line of a statement is not a D line, any continuation lines must not be D lines.

A D line can use TAB format, with the TAB expanding to one less space as the letter D already accounts for a space.

5.2.5 Increased Line Length in Fixed Source Form

Note that when this option is used the NAG Fortran Compiler no longer conforms to the Fortran language standard. The meaning of a program will change if it contains a character constant which is continued across a line boundary. A standard-conforming program containing an H-edit descriptor which is continued across a line boundary will very likely be rejected.

For new Fortran programs we recommend the use of free source form instead of this option. Free source form provides superior detection of typographical errors and is also part of the Fortran standard and thus fully portable to all standard-conforming compilers.

5.2.6 Increased Maximum Number of Continuation Lines

The Fortran 90 and 95 standards specified that the maximum number of continuation lines in fixed source form was 19, and that the maximum number of continuation lines in free source form was 39. The Fortran 2003 standard increased this to 255 lines regardless of source form.

5.2.7 Intrinsic functions with mixed-kind arguments

For SIGN, the kind of the result is the same as the kind of the first argument (which supplies the magnitude of the result), ignoring the kind of the second argument (which only supplies the sign of the result). For all the others, the kind of the result is the same as for arithmetic operations, i.e. for integers the kind with the largest number of digits, and for reals the kind with the greatest precision.

For example, if X is REAL(real32) and Y is REAL(real64):

5.2.8 ACCESS='APPEND' specifier on OPEN statement

       OPEN(17,FILE='my.log',ACCESS='APPEND')

       OPEN(17,FILE='my.log',POSITION='APPEND') ! ACCESS='SEQUENTIAL' is the default.

This is supported only as an aid to porting old programs; it should be changed to the POSITION='APPEND' specifier.

5.2.9 VAX FORTRAN TYPE statement

For example,

       TYPE *,'Hello'

       PRINT *,'Hello'

Processing a source file containing VAX FORTRAN TYPE statements with the enhanced polisher will turn all TYPE statements into PRINT statements. The ordinary polisher will not change any TYPE statements; furthermore, if one of the ambiguous forms is used, the remainder of the file will be incorrectly indented, as the ordinary polisher does not have semantic analysis and therefore assumes the ambiguous form is the beginning of a type definition.

5.2.10 Auto-skipping NAMELIST input

Normally, the NAG Fortran system raises an i/o error condition if the names do not match, but when auto-skipping namelist input is in effect, instead it skips records until it reaches the end of the file or finds a record that begins with an ampersand and the correct name.

For example, given the program

       PROGRAM asnl
         INTEGER x,y
         NAMELIST/name/x,y
         READ(*,name)
         PRINT *,'Result',x,y
       END PROGRAM

       &wrong x = 999 y = -999 /
       &name x = 123 y = 456 /

        Result 123 456

Auto-skipping namelist is controlled by runtime options. The environment variable NAGFORTRAN_RUNTIME_OPTIONS contains a comma-separated list of runtime options; auto-skipping namelist is enabled by the option autoskip_namelist or log_autoskip_namelist. The latter option produces an informative message to standard error, displaying where the namelist input occurred, for example:

       [example.f90, line 5: Looking for namelist group NAME, skipping WRONG]

5.2.11 Legacy Application Support

This option also effectively provides the extensions of allowing COMMON blocks to be initialised outside of BLOCK DATA, and of accepting VAX format octal and hexadecimal constants (these have the forms '...'O and '...'X respectively).

5.2.12 Mismatched Argument Lists

The -mismatch_all option further downgrades argument list checking so that incorrect calls to routines present in the current file being processed produce warning messages instead of error messages.

5.2.13 Double Precision Complex Extensions

If the -dcfuns option has been used, additional intrinsic functions are available (see the documentation of the option for full details). These functions have all been redundant since Fortran 90.