diff --git a/doc/static_assert.qbk b/doc/static_assert.qbk index 1b5b7be..97a7418 100644 --- a/doc/static_assert.qbk +++ b/doc/static_assert.qbk @@ -21,15 +21,28 @@ printer friendly PDF format]. [section:intro Overview and Tutorial] -The header `` supplies a single macro `BOOST_STATIC_ASSERT(x)`, -which generates a compile time error message if the integral-constant-expression `x` -is not true. In other words it is the compile time equivalent of the assert macro; +The header `` supplies two macros: + + BOOST_STATIC_ASSERT(x) + BOOST_STATIC_ASSERT_MSG(x, msg) + +Both generate a compile time error message if the integral-constant-expression `x` +is not true. In other words, they are the compile time equivalent of the assert macro; this is sometimes known as a "compile-time-assertion", but will be called a "static assertion" throughout these docs. Note that if the condition is `true`, -then the macro will generate neither code nor data - and the macro can also +then the macros will generate neither code nor data - and the macros can also be used at either namespace, class or function scope. When used in a template, the static assertion will be evaluated at the time the template is instantiated; -this is particularly useful for validating template parameters. +this is particularly useful for validating template parameters. + +If the C++0x `static_assert` feature is available, both macros will use it. +For `BOOST_STATIC_ASSERT(x)`, the error message with be a stringized version of `x`. +For `BOOST_STATIC_ASSERT_MSG(x, msg)`, the error message will be the `msg` string. + +If the C++0x `static_assert` feature is not available, `BOOST_STATIC_ASSERT_MSG(x, msg)` +will be treated as `BOOST_STATIC_ASSERT(x)`. + +The material that follows assumes the C++0x `static_assert` feature is not available. One of the aims of `BOOST_STATIC_ASSERT` is to generate readable error messages. These immediately tell the user that a library is being used in a manner that diff --git a/static_assert_test.cpp b/static_assert_test.cpp index 85457e8..3147e5c 100644 --- a/static_assert_test.cpp +++ b/static_assert_test.cpp @@ -16,12 +16,16 @@ // Namespace scope BOOST_STATIC_ASSERT(sizeof(int) >= sizeof(short)); BOOST_STATIC_ASSERT(sizeof(char) == 1); +BOOST_STATIC_ASSERT_MSG(sizeof(int) >= sizeof(short), "msg1"); +BOOST_STATIC_ASSERT_MSG(sizeof(char) == 1, "msg2"); // Function (block) scope void f() { BOOST_STATIC_ASSERT(sizeof(int) >= sizeof(short)); BOOST_STATIC_ASSERT(sizeof(char) == 1); + BOOST_STATIC_ASSERT_MSG(sizeof(int) >= sizeof(short), "msg3"); + BOOST_STATIC_ASSERT_MSG(sizeof(char) == 1, "msg4"); } struct Bob @@ -29,6 +33,8 @@ struct Bob private: // can be in private, to avoid namespace pollution BOOST_STATIC_ASSERT(sizeof(int) >= sizeof(short)); BOOST_STATIC_ASSERT(sizeof(char) == 1); + BOOST_STATIC_ASSERT_MSG(sizeof(int) >= sizeof(short), "msg5"); + BOOST_STATIC_ASSERT_MSG(sizeof(char) == 1, "msg6"); public: // Member function scope: provides access to member variables @@ -36,9 +42,11 @@ struct Bob char c; int f() { -#ifndef _MSC_VER // broken sizeof in VC6 +#if defined(_MSC_VER) && _MSC_VER < 1300 // broken sizeof in VC6 BOOST_STATIC_ASSERT(sizeof(x) >= sizeof(short)); BOOST_STATIC_ASSERT(sizeof(c) == 1); + BOOST_STATIC_ASSERT_MSG(sizeof(x) >= sizeof(short), "msg7"); + BOOST_STATIC_ASSERT_MSG(sizeof(c) == 1, "msg8"); #endif return x; } @@ -52,6 +60,7 @@ struct Bill { private: // can be in private, to avoid namespace pollution BOOST_STATIC_ASSERT(sizeof(Int) > sizeof(char)); + BOOST_STATIC_ASSERT_MSG(sizeof(Int) > sizeof(char), "msg9"); public: // Template member function scope: provides access to member variables @@ -62,10 +71,12 @@ struct Bill { BOOST_STATIC_ASSERT(sizeof(Int) == sizeof(Int2)); BOOST_STATIC_ASSERT(sizeof(Char) == sizeof(Char2)); + BOOST_STATIC_ASSERT_MSG(sizeof(Int) == sizeof(Int2), "msg10"); + BOOST_STATIC_ASSERT_MSG(sizeof(Char) == sizeof(Char2), "msg11"); } }; -void test_Bill() // BOOST_CT_ASSERTs are not triggerred until instantiated +void test_Bill() // BOOST_STATIC_ASSERTs are not triggerred until instantiated { Bill z; //Bill bad; // will not compile