Sophie: ftnchek-3.3.1-5mdv2010.0 i586

ftnchek-3.3.1-5mdv2010.0.i586.rpm

<HTML>
<HEAD>
<TITLE>Option: common</TITLE>
</HEAD>
<BODY bgcolor=white>
<A HREF="toc.html">Table of Contents</A><P>
<P>Previous: <A HREF="columns.html">-columns</A><HR><P>
<H2>Option: <font color=#FF0080>common</font></H2><P>
<A NAME="common"></A><DT><B><A HREF="common.html">-common</A>=</B><I>list</I>

<DD>
<DL COMPACT><DT><DD>
This setting controls the strictness of
checking of COMMON blocks.
By default, all warnings except <B>volatile</B> are turned on.
<P>

The <I>list</I> consists of keywords separated by commas or colons.
Since most of these warnings are on by default, include a keyword prefixed by
<B>no-</B> to turn off a particular warning.
There are three special keywords: <B>all</B> to turn on all the
warnings, <B>none</B> to turn them all
off, and <B>help</B> to print the list of all the keywords with a brief
explanation of each.
If <I>list</I> is omitted, <B><A HREF="common.html">-common</A></B> is equivalent to
<B><A HREF="common.html">-common</A>=dimensions,exact,length,type</B>,
and <B>-nocommon</B> is equivalent to
<B><A HREF="common.html">-common</A>=none</B>.
The warning keywords with their meanings are as follows:
<DL COMPACT>
<DT><B>dimensions</B>:<DD>
corresponding arrays in each declaration of a block must
agree in size and number of dimensions.  This option only has an effect
when used together with <B>exact</B>.
<DT><B>exact</B>:<DD>
the comparison of two blocks is done variable-by-variable rather than
simply requiring agreement between corresponding storage locations.
Use this if all declarations of a given COMMON block are supposed to be
identical, which is a good programming practice.
<DT><B>length</B>:<DD>
warn if different declarations of the same block are not equal in
total length.
The Fortran 77 Standard requires each named common block, but not
blank common, to be
the same length in all modules of the program.
<DT><B>type</B>:<DD>
in each declaration of a given COMMON block,
corresponding memory locations (words or bytes) must agree in data type.
If used together with <B>exact</B>, this will require that
corresponding variables agree in data type.
<DT><B>volatile</B>:<DD>
Assume that COMMON blocks are volatile.
</DL>
<P>

Many Fortran programmers assume that variables, whether
local or in COMMON, are static, i.e. that
once assigned a value, they retain that value permanently until
assigned a different value by the program.  However, in fact the
Fortran 77 Standard does not require this to be the case.
Local variables may
become undefined between activations of a module in which they are
declared.  Similarly, COMMON blocks may become undefined if no module
in which they are declared is active.  (The technical term for
entities with this behavior is ``automatic'',
but <B>ftnchek</B> uses the word ``volatile'' since it
is clearer to the nonspecialist.)  Only COMMON blocks declared
in a SAVE statement, or
declared in the main program or in a block data subprogram remain
defined as long as the program is running.  Variables and COMMON
blocks that can become undefined at some point are called volatile.
<P>

If the <B><A HREF="common.html">-common</A>=volatile</B> flag is turned on,
<B>ftnchek</B> will warn you if it finds
a volatile COMMON block.  If, at the same time, the
<B><A HREF="usage.html">-usage</A>=com-block-volatile </B> option is turned on (which is the default),
<B>ftnchek</B> will try to check whether
such a block can lose its defined status between activations of the
modules where it is declared.  <B>ftnchek</B> does not do a very good job of
this: the rule used is to see whether the block is declared in two
separated subtrees of the call tree.  For instance, this would be the
case if two modules, both called from the main program, shared a
volatile COMMON block.  A block can also become undefined between two
successive calls of the same subprogram, but <B>ftnchek</B> is not smart
enough to tell whether a subprogram can be called more than once, so
this case is not checked for.
<P>

The <B><A HREF="common.html">-common</A>=volatile</B> flag does not affect the way <B>ftnchek</B>
checks the usage of local variables.
<P>

For compatibility with previous versions of <B>ftnchek</B>,  a numeric
form of this setting is also accepted: the <I>list</I> is replaced by a
number from 0 to 3.  A value of 0 turns all the warnings off,
1 or greater turns on <B>type</B>, 2 or greater turns on <B>length</B>, and
3 turns on <B>dimensions</B> and <B>exact</B> also.  The numeric form
cannot turn on the <B>volatile</B> option.
<P>

See also: <B><A HREF="library.html">-library</A></B>, <B><A HREF="usage.html">-usage</A></B>.
</DL>

<P>
<P><HR><P>Next: <A HREF="crossref.html">-crossref</A>
</BODY></HTML>