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<TITLE>LIMITATIONS AND EXTENSIONS</TITLE>
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<A NAME="lbAK">&nbsp;</A> <H2>LIMITATIONS AND EXTENSIONS</H2>

<P>
<B>ftnchek</B> accepts ANSI standard Fortran-77 programs with some minor
limitations and numerous common extensions.
<DL COMPACT>
<DT><B>Limitations</B>:

<DD>
<DL COMPACT><DT><DD>
<B>ftnchek</B> uses only one line of lookahead when
analyzing a program into its basic syntactic elements.  If a
particular statement is difficult to identify, it may be handled
improperly if the ambiguity is not resolved on a single line.  This
limitation applies to complex constants except in DATA
statements, and to situations in which a variable name might be
confused with a keyword.  For example, if the variable name
WRITE is used for an array, then a very long
statement assigning a value
to some element of this array could be mistaken as a WRITE
statement if the equals sign is not on the same line as the word
WRITE.
<P>

The dummy arguments in statement functions are treated like ordinary
variables of the program.  That is, their scope is the entire subprogram, not
just the statement function definition.
<P>

The checking of FORMAT statements is lax, tolerating missing separators
(comma, etc.) between format descriptors in places where the Standard
requires them, and allowing <I>.d</I> fields on descriptors that should
not have them.  It does warn under <B><A HREF="f77.html">-f77</A>=format-edit-descr</B>
about nonstandard descriptor types (like
O), and supported extensions.
<P>

If a user-supplied subprogram has the same name as one of the
nonstandard intrinsic functions recognized by <B>ftnchek</B>, it must
be declared in an EXTERNAL statement in any routine that invokes
it.  Otherwise it will be subject to the checking normally given to
the intrinsic function.  Since the nonstandard intrinsics are not
standard, this EXTERNAL statement is not required by the Fortran
77 Standard.  Using the <B><A HREF="intrinsic.html">-intrinsic</A>=none</B> setting, recognition of most
nonstandard intrinsics (excepting only those needed to support the
double complex data type) can be turned off.  See the lists of
supported nonstandard intrinsic functions under the discussion of the
<B><A HREF="intrinsic.html">-intrinsic</A></B> setting above.
</DL>

<DT><B>Extensions</B>:

<DD>
<DL COMPACT><DT><DD>
All of these extensions (except lower-case characters) will generate
warnings if the relevant <B><A HREF="f77.html">-f77</A></B>
option is set.
Some of the extensions listed below are part of the Fortran-90
Standard.  These are indicated by the notation (F90).
<P>

Tabs are permitted, and translated into equivalent blanks which correspond
to tab stops every 8 columns.  The standard does not recognize tabs.
Note that some compilers allow tabs, but treat them differently.  The
treatment defined for DEC FORTRAN can be achieved using the
<B><A HREF="source.html">-source</A>=dec-tab</B> setting.
<P>

Strings may be delimited by either quote marks or apostrophes.  A
sequence of two delimiter characters is interpreted as a single
embedded delimiter character.  (F90)
<P>

Strings may contain UNIX-style backslash escape sequences.  They will
be interpreted as such if the <B><A HREF="source.html">-source</A>=unix-backslash</B> setting is given.
Otherwise the backslash character will be treated as a normal
printing character.
<P>

Source code can be in either Fortran 90 free format or traditional fixed
format.  (F90)
<P>

A semicolon is allowed as a statement separator.  (F90)
<P>

Lower case characters are permitted, and are converted internally to
uppercase except in character strings.  The standard specifies upper case only,
except in comments and strings.  (F90)
<P>

Hollerith constants are permitted, in accordance with the Fortran 77
Standard, appendix C.  They should not be used in expressions, or confused
with datatype CHARACTER.
<P>

The letter 'D' (upper or lower case) in column 1 is treated as
the beginning of a comment.  There is no option to treat such lines as
statements instead of comments.
<P>

Statements may be longer than 72 columns provided that the setting
<B><A HREF="columns.html">-columns</A></B>
was used to increase the limit.  According to the standard, all
text from columns 73 through 80 is ignored, and no line may be longer
than 80 columns.
<P>

Variable names may be longer than six characters.  The standard specifies
six as the maximum.  <B>ftnchek</B> permits names up to 31 characters
long (F90).
<P>

Variable names may contain underscores and dollar signs (or other
non-alphabetic characters as specified by the
<B><A HREF="identifier-chars.html">-identifier-chars</A></B> option).  These characters are
are treated the same as alphabetic letters.  The default type
for variables beginning with these characters is REAL.
In IMPLICIT type statements specifying a range of characters,
the dollar sign follows Z and is followed by underscore.
(Any other user-defined characters are treated the same as the dollar sign.)
Fortran 90 permits underscores in variable names.
<P>

The UNIX version tolerates the presence of preprocessor directives,
namely lines beginning with the pound sign
(#).
These are treated as comments, except for
#line
directives, which are interpreted, and are used to set the line number
and source file name for warnings and error messages.  Note that
#include
directives are not processed by <B>ftnchek</B>.  Programs that use them for
including source files should be passed through the preprocessor
before being input to <B>ftnchek</B>.
As noted below, <B>ftnchek</B> does process
INCLUDE statements, which have a different syntax.
An optional program, <B><A HREF="http://localhost/cgi-bin/man/man2html?1L+ftnpp">ftnpp</A></B>(1L) (available separately)
provides  preprocessing that properly handles
INCLUDE files.
<P>

The Fortran 90 DO ...  ENDDO control structure is permitted.
The CYCLE and EXIT statements are accepted.  All of these may
have an optional do-construct name, but construct names are not checked for
consistency. (F90)
<P>

The Fortran 90 SELECT CASE construct is accepted. (F90)
<P>

Construct names are also accepted on IF, THEN, ELSE,
ENDIF and SELECT CASE statements. (F90)
<P>

The ACCEPT and TYPE statements (for terminal I/O) are
permitted, with the same syntax as PRINT.
<P>

The so-called ``Cray pointer'' syntax is tolerated. It is not the same as the
Fortran 90 POINTER statement.  There is no real checking
of the statement other than basic syntax.
The form of this statement is
<BR>


POINTER (<I>pointer</I>, <I>pointee</I>)
[,(<I>pointer</I>, <I>pointee</I>)]

<BR>

The pointer variables are assigned a data type of INTEGER *4.
Usage checking of the pointee variables is suppressed, since in
practice they are accessed indirectly via the pointers.
<P>

Statements may have any number of continuation lines.  The Fortran 77
and Fortran 90 standards allow a maximum of 19 in fixed source form.
The Fortran 90 standard allows a maximum of 39 in free source form.
<P>

Relational (comparison) operators composed of punctuation, namely: &lt;
&lt;= == /= &gt; &gt;= are allowed.  (F90)
<P>

Inline comments, beginning with an exclamation mark, are
permitted.  (F90)
<P>

NAMELIST I/O is supported.  The syntax is the same as in Fortran 90.
<P>

FORMAT statements can contain a dollar sign to indicate suppression of
carriage-return.
An integer expression enclosed in angle brackets can be used anywhere in a
FORMAT statement where
the Fortran 77 Standard allows an integer constant (except for the length of a
Hollerith constant),
to provide a run-time value for a repeat specification or field width.
<P>

Nonstandard keywords are allowed in I/O statements,
corresponding to those in VMS Fortran.
<P>

The IMPLICIT NONE statement is supported.  The meaning of this
statement is that all variables must have their data types explicitly
declared.  Rather than flag the occurrences of such variables with
syntax error messages, <B>ftnchek</B> waits till the end of the module,
and then prints out a list of all undeclared variables,
as it does for the <B><A HREF="declare.html">-declare</A></B> option.  (F90)
<P>

Data types INTEGER, REAL, COMPLEX, and
LOGICAL are allowed to have an optional precision specification in
type declarations.  For instance, REAL*8 means an 8-byte
floating point data type.  The REAL*8 datatype is not
necessarily considered equivalent to DOUBLE PRECISION,
depending on the <B><A HREF="wordsize.html">-wordsize</A></B> setting.
The Fortran 77 Standard allows
a length specification only for CHARACTER data.
<P>

<B>ftnchek</B> supports the DOUBLE COMPLEX type
specification for a complex quantity whose real and imaginary parts
are double precision.  Mixed-mode arithmetic involving
single-precision complex with double-precision real data,
prohibited under the Standard, yields a double complex result.
<P>

There is limited support for Fortran 90 attribute-based type
declarations.  This style of declaration is distinguished by the use
of a double colon (::) between the list of attributes and the list of
declared variables.  The features supported may be
adequate for novice programmers, but are not yet sufficient for
professional-quality Fortran 90 programs.  I hope to add
support for more features in future releases.  I invite volunteers to
assist in this task.  See the ToDo file in the source code
distribution for details.
The attributes currently accepted, besides all
the usual data types, are DIMENSION, EXTERNAL,
INTRINSIC, PARAMETER, and SAVE.  The new form of
declaration also allows assignment of values to the variables
declared.  At present, the (LEN=<I>value</I>) form of specifying
character lengths is also accepted.  Kind specifications, using
(KIND=<I>value</I>) are parsed but are not processed: all kinds
are treated as default kind.  Also, there is little checking of these
declarations beyond basic syntax.
<P>

Many commonly found nonstandard intrinsic functions are provided.  See
the discussion of <B><A HREF="intrinsic.html">-intrinsic</A></B> for a list of functions and how to
control which ones are recognized.
<P>

Argument checking is not tight for those nonstandard intrinsics
that take arrays or mixed argument types.
<P>

<B>ftnchek</B> permits the INCLUDE statement, which causes
inclusion of the text of the given file.  The syntax is
<BR>


INCLUDE '<I>filename</I>'

<BR>

This is compatible with Fortran 90.
If the <B><A HREF="source.html">-source</A>=vms-include</B> option is given, <B>ftnchek</B> follows
VMS conventions with respect to this statement: it assumes a default
extension of <I>.for</I> if no filename extension is given, and
allows the qualifier /[NO]LIST following the filename, to
control the listing of the included file.  There is no support for
including VMS text modules.
<P>

In diagnostic output relating to items contained in include
files, the location of the error is specified by both
its location in the include file and the location in the parent file
where the file was included.
<P>

<B>ftnchek</B> accepts PARAMETER statements which lack
parentheses.  These will be warned about if the
<B><A HREF="f77.html">-f77</A>=param-noparen</B> flag is given.
<P>

<B>ftnchek</B> accepts PARAMETER definitions that involve
intrinsic functions
and exponentiation by a non-integer exponent.  Both of these cases are
prohibited by the Fortran 77
Standard, and will be warned about if the <B><A HREF="f77.html">-f77</A>=param-intrinsic</B>
flag is given.  If an intrinsic function value
is a compile-time integer constant,
<B>ftnchek</B> will evaluate it.  This allows better checking if the
parameter is used in declaring array sizes.  Fortran 90 allows
intrinsic functions in PARAMETER definitions.
<P>

The intrinsic functions that are evaluated are:

<CENTER><TABLE>
<TR VALIGN=top><TD>ABS</TD><TD>IABS</TD><TD>DIM</TD><TD>IDIM</TD><TD>MAX<BR></TD></TR>
<TR VALIGN=top><TD>MAX0</TD><TD>MIN</TD><TD>MIN0</TD><TD>MOD</TD><TD>SIGN<BR></TD></TR>
<TR VALIGN=top><TD>ISIGN</TD><TD>LEN</TD><TD>ICHAR</TD><TD>INDEX</TD><TD><BR></TD></TR>
</TABLE></CENTER>


<BR>

The functions of integer arguments are evaluated only if the arguments
are integer constant expressions.  (These may involve integer
constants, parameters, and evaluated intrinsic functions.)  The
function LEN is evaluated if its argument is an expression
involving only character constants and variables whose length is not
adjustable.  The functions ICHAR and INDEX are evaluated
only if the arguments are character constants.  <B>ftnchek</B> gives a
warning if it needs the value of some intrinsic function that is not
evaluated.
</DL>



</DL>
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