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<HTML>
<HEAD>
<TITLE>Option: usage</TITLE>
</HEAD>
<BODY>
<A HREF="toc.html">Table of Contents</A><P>
<P>Previous: <A HREF="truncation.html">-truncation</A><HR><P>
<H2>Option: <font color=#FF0080>usage</font></H2><P>
<A NAME="usage"></A><DT><B><A HREF="usage.html">-usage</A>=</B><I>list</I> </DT>
<DD>Warn about unused or possible uninitialized
variables, unused common blocks, and unused or undefined subprograms. By
default, all warnings are turned on. <blockquote></DD>
</DL>
<P>
This setting provides detailed control
over the warnings about possible usage errors. The <I>list </I> consists of keywords
separated by commas or colons. Since all 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 about usage, <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="usage.html">-usage</A> </B> is equivalent
to <B><A HREF="usage.html">-usage</A>=all </B>, and <B>-nousage </B> is equivalent to <B><A HREF="usage.html">-usage</A>=none </B>. These warnings
cover four main categories of objects: subprogram dummy arguments, common
blocks and variables, subprograms and functions, and local variables.
Warnings include undefined items, multiply defined items, unused items,
etc. The warning keywords with their meanings are as follows:
<DL>
<DT><B>arg-alias</B>:
</DT>
<DD>a scalar dummy argument is actually the same as another and is (or may
be) modified. The Fortran 77 standard (section 15.9.3.6) prohibits modifying
an argument that is aliased to another. </DD>
<DT><B>arg-array-alias</B>: </DT>
<DD>a dummy argument
which is an array or array element is in the same array as another and
is modified. This flag is similar to <B>arg-alias </B> but provides separate control
over array arguments. It is harder to tell if aliasing is occurring in
the case of arrays, so if <B>ftnchek </B> gives too many false warnings, this
flag allows the array-related ones to be turned off without suppressing
the warnings for scalars. </DD>
<DT><B>arg-common-alias</B>: </DT>
<DD>a scalar dummy argument is the
same as a common variable in the subprogram, and either is modified. This
is also prohibited by the Fortran 77 standard. If common checking is not
exact (see the <B><A HREF="common.html">-common</A> </B> setting), it is harder to tell if aliasing is occurring,
so the warning is given if the variable is anywhere in a common block
that is declared by the subprogram. </DD>
<DT><B>arg-common-array-alias</B>: </DT>
<DD>a dummy argument
which is an array or array element is in the same array as a common variable,
and either is modified. If common checking is not exact, the variable
can be anywhere in a common block that is declared by the subprogram. </DD>
<DT><B>arg-const-modified</B>:
</DT>
<DD>a subprogram modifies an argument which is a constant or an expression.
Such an action could cause anomalous behavior of the program. </DD>
<DT><B>com-block-unused</B>:
</DT>
<DD>a common block is declared but none of the variables in it are used by
any subprogram. This warning is suppressed if the common strictness setting
is 0. </DD>
<DT><B>com-block-volatile</B>: </DT>
<DD>a common block may lose the definition of its
contents if common blocks are volatile. This option only has an effect
if the <B><A HREF="common.html">-common</A>=volatile </B> flag is in effect. See the discussion of the <B><A HREF="common.html">-common</A>
</B> setting above. </DD>
<DT><B>com-var-set-unused</B>: </DT>
<DD>a common variable is assigned a value,
but its value is not used by any subprogram. This warning is suppressed
if the common strictness setting is 0. </DD>
<DT><B>com-var-uninitialized</B>: </DT>
<DD>a common variable's
value is used in some subprogram, but is not set anywhere. Unfortunately,
<B>ftnchek </B> does not do a thorough enough analysis of the calling sequence
to know which routines are called before others. So warnings about this
type of error will only be given for cases in which a variable is used
in some routine but not set in any other routine. Checking of individual
COMMON variables is done only if the <B><A HREF="common.html">-common</A> </B> setting is 3 (variable by
variable agreement). This warning is suppressed if the common strictness
setting is 0. </DD>
<DT><B>com-var-unused</B>: </DT>
<DD>a common variable is declared but not used
by any subprogram. This warning is suppressed if the common strictness
setting is 0. </DD>
<DT><B>ext-multiply-defined</B>: </DT>
<DD>an external (a subroutine or function)
is defined more than once. Definition of an external means providing the
body of its source code. </DD>
<DT><B>ext-declared-only</B>: </DT>
<DD>a name is declared in an EXTERNAL
statement in some module, but is not defined or used anywhere. </DD>
<DT><B>ext-undefined</B>:
</DT>
<DD>an external is used (invoked) but not defined anywhere. This option is
equivalent to the <B><A HREF="extern.html">-extern</A>al </B> flag. If the subprogram is invoked more than
once, those invocations will still be checked for consistency. </DD>
<DT><B>ext-unused</B>:
</DT>
<DD>an external is defined (its subprogram body is present) but it is not
used. A subprogram is considered unused even if it is invoked by some
other subprogram, if it cannot be called from any thread of execution
starting with the main program. The agreement of the subprogram's arguments
with its invocations is still checked even if this warning is turned off.
If there is no main program, then this warning is issued only if the subprogram
is not invoked anywhere. This warning is suppressed in library mode, but
library mode has the additional effect of suppressing argument checking
for unused routines. </DD>
<DT><B>var-set-unused</B>: </DT>
<DD>a local variable is assigned a value,
but that value is not used. </DD>
<DT><B>var-uninitialized</B>: </DT>
<DD>a local variable's value
may be used before it is assigned. Sometimes <B>ftnchek </B> makes a mistake in
the warnings about local variable usage. Usually it errs on the side of
giving a warning where no problem exists, but in rare cases it may fail
to warn where the problem does exist. See the section on Bugs for examples.
If variables are equivalenced, the rule used by <B>ftnchek </B> is that a reference
to any variable implies the same reference to all variables it is equivalenced
to. For arrays, the rule is that a reference to any array element is treated
as a reference to all elements of the array. </DD>
<DT><B>var-unused</B>: </DT>
<DD>a local variable
is declared (for instance, in a type declaration) but is not used in the
module. </DD>
</DL>
<P>
Note: In versions of <B>ftnchek </B> prior to 2.10, the <B><A HREF="usage.html">-usage</A> </B> flag took
a numeric argument instead of a list of options. For the sake of users
who may have written scripts invoking <B>ftnchek </B> in this way, the numeric
form is still accepted. The numeric setting is composed of three digits.
The first digit (hundreds place) controls warnings about subprograms
(functions and subroutines), the second digit (tens place) warnings about
common blocks and common variables,, and the third digit (ones place)
warnings about local variables. Each digit controls warnings according
to the convention that a 1 means warn about undefined items and variables
that are used before set, a 2 means warn about items that are unused,
and a 3 means warn about both types. These numbers are now converted to
the appropriate values for the above-listed keywords, except for <B>com-block-volatile
</B>, which is not affected by the numeric argument. <P>
See also: <B><A HREF="common.html">-common</A> </B>, <B><A HREF="declare.html">-declare</A>
</B>, <B><A HREF="extern.html">-extern</A> </B>, <B><A HREF="library.html">-library</A> </B>. </blockquote>
<P>
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