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C++ Producer Guide: Error catalogue
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<BODY TEXT="#000000" BGCOLOR="#FFFFFF" LINK="#0000FF" VLINK="#400080" ALINK="#FF0000">
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<H1>C++ Producer Guide</H1>
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<H3>March 1998</H3>
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<A HREF="parse.html"><IMG SRC="../images/next.gif" ALT="next section"></A>
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<IMG SRC="../images/no_index.gif" ALT="document index"><P>
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<HR>
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<H2>3.3. Error catalogue</H2>
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<P>
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This section describes the error catalogue which lies at the heart
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of the C++ producer's error reporting routines. The full
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<A HREF="error1.html">error catalogue syntax</A> is given as an annex.
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A typical entry in the catalogue is as follows:
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<PRE>
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class_union_deriv ( CLASS_TYPE: ct )
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{
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USAGE: serious
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PROPERTIES: ansi
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KEY (ISO) "9.5"
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KEY (STANDARD) "The union '"ct"' can't have base classes"
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}
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</PRE>
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This defines an error, <CODE>class_union_deriv</CODE>, which takes
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a single parameter <CODE>ct</CODE> of type <CODE>CLASS_TYPE</CODE>.
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The severity of this error is <CODE>serious</CODE>; that is to say,
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a constraint error. The error property <CODE>ansi</CODE> indicates
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that the error arises from the ISO C++ standard, the associated
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<CODE>ISO</CODE> key indicating section 9.5. Finally the text to
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be printed for this error, including a reference to <CODE>ct</CODE>,
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is given. Looking up section 9.5 in the ISO C++ standard reveals
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the corresponding constraint in paragraph 1:
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<BLOCKQUOTE>
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<I>A union shall not have base classes.</I>
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</BLOCKQUOTE>
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Each constraint within the ISO C++ standard has a corresponding error
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in this way. The errors are named in a systematic fashion using the
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section names used in the draft standard. For example, section 9.5
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is called <CODE>class.union</CODE>, so all the constraint errors arising
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from this section have names of the form <CODE>class_union_*</CODE>.
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These error names can be used in the <A HREF="pragma.html#low">low
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level directives</A> such as:
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<PRE>
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#pragma TenDRA++ error "class_union_deriv" <I>allow</I>
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</PRE>
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to modify the error severity. The effect of reducing the severity
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of a constraint error in this way is undefined.
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</P>
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<P>
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In addition to the obvious error severity levels, <CODE>serious</CODE>,
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<CODE>warning</CODE> and <CODE>none</CODE>, the error catalogue specifies
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a list of optional severity levels along with their default values.
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For example, the entry:
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<PRE>
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link_incompat = serious
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</PRE>
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sets up an option named <CODE>link_incompat</CODE> which is a constraint
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error by default. Errors with this severity, such as:
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<PRE>
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dcl_stc_external ( LONG_ID: id, PTR_LOC: loc )
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{
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USAGE: link_incompat
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PROPERTIES: ansi
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KEY (ISO) "7.1.1"
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KEY (STANDARD) "'"id"' previously declared with external
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linkage (at "loc")"
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}
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</PRE>
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are therefore constraint errors. The severity associated with
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<CODE>link_incompat</CODE> can be modified either
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<A HREF="pragma.html#low">directly</A>, using the directive:
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<PRE>
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#pragma TenDRA++ option "link_incompat" <I>allow</I>
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</PRE>
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or <A HREF="pragma.html#linkage">indirectly</A> using the directive:
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<PRE>
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#pragma TenDRA incompatible linkage <I>allow</I>
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</PRE>
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the effect being to modify the severity of the associated error messages.
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</P>
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<P>
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The error catalogue is processed by a simple tool,
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<CODE>make_err</CODE>, which generates C code which is compiled into
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the C++ producer. Each error in the catalogue is assigned a number
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(there are currently 873 errors in the catalogue) which gives an index
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into an automatically generated table of error information. It is
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this error number, together with a list of error arguments, which
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forms the associated <A HREF="alg.html#err"><CODE>ERROR</CODE> object</A>.
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<CODE>make_err</CODE> generates a macro for each error in the catalogue
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which takes arguments of the appropriate types (which may be statically
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checked) and creates an <CODE>ERROR</CODE> object. For example, for
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the entry above this macro takes the form:
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<PRE>
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ERROR ERR_class_union_deriv ( CLASS_TYPE ) ;
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</PRE>
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These macros hide the error catalogue numbers from the rest of the
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C++ producer.
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</P>
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<P>
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It is also possible to join a number of simple <CODE>ERROR</CODE>
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objects to form a single composite <CODE>ERROR</CODE>. The severity
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of the composite error is the maximum of the severities of the component
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errors. To this purpose a dummy error severity level <CODE>whatever</CODE>
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is introduced which is less severe than any other level. This is
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intended for use with error messages which are only ever used to add
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information to existing errors, and which inherit their severity level
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from the main error.
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</P>
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<P>
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The text of a simple error message can be found in the table of error
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information. The text contains certain escape sequences indicating
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where the error arguments are to be printed. For example,
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<CODE>%1</CODE> indicates the second argument. The error argument
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sorts - what is referred to as the error signature - is also stored
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in the table of error information as an array of characters, each
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corresponding to an <CODE>ERR_KEY_</CODE><I>type</I> macro. The producer
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defines printing routines for each of the types given by these values,
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and calls the appropriate routine to print the argument.
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</P>
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<P>
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There are several command-line options which can be used to modify
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the form in which the error message is printed. The default format
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is as follows:
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<PRE>
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"file.C", line 42: Error:
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[ISO 9.5]: The union 'U' can't have base classes.
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</PRE>
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The ISO section number can be suppressed using <CODE>-m-s</CODE>.
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The <CODE>-mc</CODE> option causes the source code line giving rise
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to the error to be printed as part of the message, with <CODE>!!!!</CODE>
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marking the position of the error within the line. The <CODE>-me</CODE>
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option causes the error name, <CODE>class_union_deriv</CODE>, to be
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printed as part of the message. The <CODE>-ml</CODE> option causes
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the full file location, including the list of <CODE>#include</CODE>
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directives used in reaching the file, to be printed. The <CODE>-mt</CODE>
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option causes <CODE>typedef</CODE> names to be used when printing
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types, rather than expanding to the type definition.
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</P>
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<HR>
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<P><I>Part of the <A HREF="../index.html">TenDRA Web</A>.<BR>Crown
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Copyright © 1998.</I></P>
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