Changes between Version 19 and Version 20 of Guidelines/WarningsGuidelines

Timestamp:

Mar 26, 2011, 10:49:05 PM (12 years ago)

Author:

phorgan1

Comment:

--

Guidelines/WarningsGuidelines

@@ -726 +726 @@
   Available since GCC version 4.6, this pragma lets you remember diagnostic options in place at a particular time.  This pragma can occur on any line of a file.  The number of nested pushes is limited only by the size of memory and the size of an int index into the diagnostic information.
  #pragma GCC diagnostic pop::
-  Available since GCC version 4.6, this pragma lets you restore diagnostic options that were remembered by a diagnostic push. This pragma can occur on any line of a file.  The number of pops is limited by memory and the size of an int index into the diagnostic information.  At a pop information is moved from the table used by push into a history.  An unbalanced pop, i.e. popping when nothing is on the stack is harmless and will simply reassert the user's command line diagnostic choices.
+  Available since GCC version 4.6, this pragma lets you restore diagnostic options that were remembered by a diagnostic push. This pragma can occur on any line of a file.  The number of pops is limited by memory and the size of an int index into the diagnostic information.  At a pop information is moved from the table used by push into a history.  An unbalanced pop, i.e. popping when nothing is on the stack is harmless and will simply reassert the user's command line diagnostic choices.    Be careful, though, that you don't pop to soon.  In this example:
+{{{
+foo()
+{
+    int unused,i;
+    i=3;
+}
+}}}
+We might want to suppress the unused variable like this:
+{{{
+foo()
+{
+#pragma GCC diagnostic push
+#pragma GCC diagnostic "-Wunused-variable"
+    int unused,i;
+#pragma GCC diagnostic pop
+    i=3;
+}
+}}}
+and then be surprised that we still get a warning about an unused variable.  The reason is, that GCC doesn't know the variable is unused until it hits the closing brace.  That means the pop has to come after the closing brace:
+{{{
+foo()
+{
+#pragma GCC diagnostic push
+#pragma GCC diagnostic "-Wunused-variable"
+    int unused,i;
+    i=3;
+}
+#pragma GCC diagnostic pop
+}}}
+
  #pragma GCC diagnostic [warning|error|ignored] OPTION::
   From GCC version 4.2.4 and before GCC version 4.6 this could be specified at file scope outside of any functions, classes, unions, structs, or methods, to change the behavior when a particular class of error was seen.  For GCC version 4.6 and later, it can be put in any line of a file, and affects from that position forward.  For any supported version, it only works with warnings that have explicit -W arguments, use -fdiagnostic-show-option to find out which one to use.  An example: #pragma GCC diagnostic ignored "-Wdeprecated-declarations"