+|
+
+ BOOST_FALLTHROUGH
+
+ |
+
+
+ The BOOST_FALLTHROUGH macro can be used to annotate implicit fall-through
+ between switch labels:
+
+switch (x) {
+case 40:
+case 41:
+ if (truth_is_out_there) {
+ ++x;
+ BOOST_FALLTHROUGH;
+
+ } else {
+ return x;
+ }
+ case 42:
+ ...
+
+
+ As shown in the example above, the BOOST_FALLTHROUGH macro should
+ be followed by a semicolon. It is designed to mimic control-flow
+ statements like 'break;', so it can be placed in most places where
+ 'break;' can, but only if there are no statements on the execution
+ path between it and the next switch label.
+
+
+ When compiled with Clang >3.2 in C++11 mode, the BOOST_FALLTHROUGH
+ macro is expanded to [[clang::fallthrough]]
+ attribute, which is analysed when performing switch labels fall-through
+ diagnostic ('-Wimplicit-fallthrough'). See clang documentation
+ on language extensions for details.
+
+
+ When used with unsupported compilers, the BOOST_FALLTHROUGH macro
+ has no effect on diagnostics.
+
+
+ In either case this macro has no effect on runtime behavior and
+ performance of code.
+
+ |
+
+
|
BOOST_EXPLICIT_TEMPLATE_TYPE(t) BOOST_EXPLICIT_TEMPLATE_NON_TYPE(t,v) BOOST_APPEND_EXPLICIT_TEMPLATE_TYPE(t) BOOST_APPEND_EXPLICIT_TEMPLATE_NON_TYPE(t,v)
diff --git a/doc/html/index.html b/doc/html/index.html
index bdf89c1b..a30cd0fd 100644
--- a/doc/html/index.html
+++ b/doc/html/index.html
@@ -951,7 +951,7 @@
-Last revised: February 19, 2013 at 16:25:18 GMT |
+Last revised: April 18, 2013 at 17:44:14 GMT |
|
diff --git a/doc/macro_reference.qbk b/doc/macro_reference.qbk
index 6b424546..a96a16c9 100644
--- a/doc/macro_reference.qbk
+++ b/doc/macro_reference.qbk
@@ -862,6 +862,41 @@ struct foo{
Normally evaluates to nothing, but evaluates to return x; if the compiler
requires a return, even when it can never be reached.
]]
+[[`BOOST_FALLTHROUGH`][
+The BOOST_FALLTHROUGH macro can be used to annotate implicit fall-through
+between switch labels:
+``
+ switch (x) {
+ case 40:
+ case 41:
+ if (truth_is_out_there) {
+ ++x;
+ BOOST_FALLTHROUGH; // Use instead of/along with annotations in
+ // comments.
+ } else {
+ return x;
+ }
+ case 42:
+ ...
+``
+As shown in the example above, the BOOST_FALLTHROUGH macro should be
+followed by a semicolon. It is designed to mimic control-flow statements
+like 'break;', so it can be placed in most places where 'break;' can, but
+only if there are no statements on the execution path between it and the
+next switch label.
+
+When compiled with Clang >3.2 in C++11 mode, the BOOST_FALLTHROUGH macro is
+expanded to `[[clang::fallthrough]]` attribute, which is analysed when
+performing switch labels fall-through diagnostic ('-Wimplicit-fallthrough').
+See clang [@http://clang.llvm.org/docs/LanguageExtensions.html#clang__fallthrough
+documentation on language extensions for details.]
+
+When used with unsupported compilers, the BOOST_FALLTHROUGH macro has no
+effect on diagnostics.
+
+In either case this macro has no effect on runtime behavior and performance
+of code.
+]]
[[`BOOST_EXPLICIT_TEMPLATE_TYPE(t)`
`BOOST_EXPLICIT_TEMPLATE_NON_TYPE(t,v)`
`BOOST_APPEND_EXPLICIT_TEMPLATE_TYPE(t)`
diff --git a/include/boost/config/compiler/clang.hpp b/include/boost/config/compiler/clang.hpp
index 209c9007..4bc4feeb 100644
--- a/include/boost/config/compiler/clang.hpp
+++ b/include/boost/config/compiler/clang.hpp
@@ -38,6 +38,16 @@
# define BOOST_SYMBOL_VISIBLE __attribute__((__visibility__("default")))
#endif
+//
+// The BOOST_FALLTHROUGH macro can be used to annotate implicit fall-through
+// between switch labels.
+//
+#if __cplusplus >= 201103L && defined(__has_warning)
+# if __has_feature(cxx_attributes) && __has_warning("-Wimplicit-fallthrough")
+# define BOOST_FALLTHROUGH [[clang::fallthrough]]
+# endif
+#endif
+
#if !__has_feature(cxx_auto_type)
# define BOOST_NO_CXX11_AUTO_DECLARATIONS
# define BOOST_NO_CXX11_AUTO_MULTIDECLARATIONS
diff --git a/include/boost/config/suffix.hpp b/include/boost/config/suffix.hpp
index d4524812..c0928dde 100644
--- a/include/boost/config/suffix.hpp
+++ b/include/boost/config/suffix.hpp
@@ -883,6 +883,16 @@ namespace std{ using ::type_info; }
# define BOOST_NOEXCEPT_IF(Predicate) noexcept((Predicate))
# define BOOST_NOEXCEPT_EXPR(Expression) noexcept((Expression))
#endif
+//
+// Helper macro BOOST_FALLTHROUGH
+// Fallback definition of BOOST_FALLTHROUGH macro used to mark intended
+// fall-through between case labels in a switch statement. We use a definition
+// that requires a semicolon after it to avoid at least one type of misuse even
+// on unsupported compilers.
+//
+#ifndef BOOST_FALLTHROUGH
+# define BOOST_FALLTHROUGH ((void)0)
+#endif
//
// constexpr workarounds
diff --git a/test/Jamfile.v2 b/test/Jamfile.v2
index 314ab4bd..ba8f7804 100644
--- a/test/Jamfile.v2
+++ b/test/Jamfile.v2
@@ -65,4 +65,5 @@ test-suite config
]
[ compile-fail threads/test_thread_fail1.cpp ]
[ compile-fail threads/test_thread_fail2.cpp ]
+ [ compile boost_fallthrough_test.cpp : clang:"-std=c++11 -Wimplicit-fallthrough" on all ]
;
diff --git a/test/boost_fallthrough_test.cpp b/test/boost_fallthrough_test.cpp
new file mode 100644
index 00000000..3fabe351
--- /dev/null
+++ b/test/boost_fallthrough_test.cpp
@@ -0,0 +1,20 @@
+// Use, modification and distribution are subject to the
+// Boost Software License, Version 1.0. (See accompanying file
+// LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+
+#include
+
+int test(int n)
+{
+ switch (n)
+ {
+ case 0:
+ n++;
+ BOOST_FALLTHROUGH;
+ case 1:
+ n++;
+ break;
+ }
+ return n;
+}
+
diff --git a/test/config_info.cpp b/test/config_info.cpp
index 7381bd30..b4b435d1 100644
--- a/test/config_info.cpp
+++ b/test/config_info.cpp
@@ -1100,27 +1100,6 @@ void print_boost_macros()
PRINT_MACRO(BOOST_NO_USING_TEMPLATE);
PRINT_MACRO(BOOST_NO_VOID_RETURNS);
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
// END GENERATED BLOCK
PRINT_MACRO(BOOST_INTEL);
@@ -1132,6 +1111,7 @@ void print_boost_macros()
PRINT_MACRO(BOOST_STATIC_CONSTEXPR);
PRINT_MACRO(BOOST_NOEXCEPT);
PRINT_MACRO(BOOST_FORCEINLINE);
+ PRINT_MACRO(BOOST_FALLTHROUGH);
}
void print_separator()
|