Re: [PATCH] init-if-undefined command

Andrew STUBBS
2005-11-30T14:15:14Z

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Here is another version with the various help strings updated.

I have rewritten the main help because I noticed it did not start with
something suitable for 'help data'. I also added a little more
information about its exact behaviour.

I hope this is better now.

Andrew Stubbs

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2005-11-30 Andrew Stubbs <andrew.stubbs@st.com>

* value.c (init_if_undefined_command): New function.
(_initialize_values): Add command init-if-undefined.

doc/
* gdb.texinfo (Convenience variables): Add init-if-undefined command.

Index: src/gdb/value.c
===================================================================
--- src.orig/gdb/value.c 2005-11-29 16:35:46.000000000 +0000
+++ src/gdb/value.c 2005-11-30 12:46:34.000000000 +0000
@@ -727,6 +727,47 @@ show_values (char *num_exp, int from_tty

static struct internalvar *internalvars;

+/* If the variable does not already exist create it and give it the value given.
+ If no value is given then the default is zero. */
+static void
+init_if_undefined_command (char* args, int from_tty)
+{
+ struct internalvar* intvar;
+
+ /* Parse the expression - this is taken from set_command(). */
+ struct expression *expr = parse_expression (args);
+ register struct cleanup *old_chain =
+ make_cleanup (free_current_contents, &expr);
+
+ /* Validate the expression.
+ Was the expression an assignment?
+ Or even an expression at all? */
+ if (expr->nelts == 0 || expr->elts[0].opcode != BINOP_ASSIGN)
+ {
+ printf_unfiltered ("Init-if-undefined requires an assignment expression.\n");
+ do_cleanups (old_chain);
+ return;
+ }
+
+ /* Extract the variable from the parsed expression.
+ In the case of an assign the lvalue will be in elts[1] and elts[2]. */
+ if (expr->elts[1].opcode != OP_INTERNALVAR)
+ {
+ printf_unfiltered ("The first parameter to init-if-undefined should be a GDB variable\n");
+ do_cleanups (old_chain);
+ return;
+ }
+ intvar = expr->elts[2].internalvar;
+
+ /* Only evaluate the expression if the lvalue is void.
+ This may still fail if the expresssion is invalid. */
+ if (TYPE_CODE (value_type (intvar->value)) == TYPE_CODE_VOID)
+ evaluate_expression (expr);
+
+ do_cleanups (old_chain);
+}
+
+
/* Look up an internal variable with name NAME. NAME should not
normally include a dollar sign.

@@ -1639,4 +1680,11 @@ A few convenience variables are given va
add_cmd ("values", no_class, show_values,
_("Elements of value history around item number IDX (or last ten)."),
&showlist);
+
+ add_com ("init-if-undefined", class_vars, init_if_undefined_command, _("\
+Initialize a convenience variable if necessary.\n\
+init-if-undefined VARIABLE = EXPRESSION\n\
+Set an internal VARIABLE to the result of the EXPRESSION if it does not\n\
+exist or does not contain a value. The EXPRESSION is not evaluated if the\n\
+VARIABLE is already initialized."));
}
Index: src/gdb/doc/gdb.texinfo
===================================================================
--- src.orig/gdb/doc/gdb.texinfo 2005-11-29 16:36:23.000000000 +0000
+++ src/gdb/doc/gdb.texinfo 2005-11-30 12:24:23.000000000 +0000
@@ -6131,6 +6131,18 @@ variable, when used as an expression, ha
@item show convenience
Print a list of convenience variables used so far, and their values.
Abbreviated @code{show conv}.
+
+@kindex init-if-undefined
+@cindex convenience variables, initializing
+@item init-if-undefined $@var{variable} = @var{expression}
+Set a convenience variable if it has not already been set. This is useful
+for user-defined commands that keep some state. It is similar, in concept,
+to using local static variables with initializers in C (except that
+convenience variables are global). It can also be used to allow users to
+override default values used in a command script.
+
+If the variable is already defined then the expression is not evaluated so
+any side-effects do not occur.
@end table

One of the ways to use a convenience variable is as a counter to be