+/* Like lex_macro_node, but read the input from STR. */
+static cpp_hashnode *
+lex_macro_node_from_str (cpp_reader *pfile, const char *str)
+{
+ size_t len = strlen (str);
+ uchar *buf = (uchar *) alloca (len + 1);
+ cpp_hashnode *node;
+
+ memcpy (buf, str, len);
+ buf[len] = '\n';
+ cpp_push_buffer (pfile, buf, len, true);
+ node = lex_macro_node (pfile, true);
+ _cpp_pop_buffer (pfile);
+
+ return node;
+}
+
+/* If STR is a defined macro, return its definition node, else return NULL. */
+cpp_macro *
+cpp_push_definition (cpp_reader *pfile, const char *str)
+{
+ cpp_hashnode *node = lex_macro_node_from_str (pfile, str);
+ if (node && node->type == NT_MACRO)
+ return node->value.macro;
+ else
+ return NULL;
+}
+
+/* Replace a previous definition DFN of the macro STR. If DFN is NULL,
+ then the macro should be undefined. */
+void
+cpp_pop_definition (cpp_reader *pfile, const char *str, cpp_macro *dfn)
+{
+ cpp_hashnode *node = lex_macro_node_from_str (pfile, str);
+ if (node == NULL)
+ return;
+
+ if (pfile->cb.before_define)
+ pfile->cb.before_define (pfile);
+
+ if (node->type == NT_MACRO)
+ {
+ if (pfile->cb.undef)
+ pfile->cb.undef (pfile, pfile->directive_line, node);
+ if (CPP_OPTION (pfile, warn_unused_macros))
+ _cpp_warn_if_unused_macro (pfile, node, NULL);
+ }
+ if (node->type != NT_VOID)
+ _cpp_free_definition (node);
+
+ if (dfn)
+ {
+ node->type = NT_MACRO;
+ node->value.macro = dfn;
+ if (! ustrncmp (NODE_NAME (node), DSC ("__STDC_")))
+ node->flags |= NODE_WARN;
+
+ if (pfile->cb.define)
+ pfile->cb.define (pfile, pfile->directive_line, node);
+ }
+}
+
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