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Assertion Macros, <boost/assert.hpp>

BOOST_ASSERT

The header <boost/assert.hpp> defines the macro BOOST_ASSERT, which is similar to the standard assert macro defined in <cassert>. The macro is intended to be used in both Boost libraries and user code.

  • By default, BOOST_ASSERT(expr) expands to assert(expr).

  • If the macro BOOST_DISABLE_ASSERTS is defined when <boost/assert.hpp> is included, BOOST_ASSERT(expr) expands to ((void)0), regardless of whether the macro NDEBUG is defined. This allows users to selectively disable BOOST_ASSERT without affecting the definition of the standard assert.

  • If the macro BOOST_ENABLE_ASSERT_HANDLER is defined when <boost/assert.hpp> is included, BOOST_ASSERT(expr) expands to

    (BOOST_LIKELY(!!(expr))? ((void)0): ::boost::assertion_failed(#expr,
    BOOST_CURRENT_FUNCTION, __FILE__, __LINE__))

    That is, it evaluates expr and if it’s false, calls ::boost::assertion_failed(#expr, BOOST_CURRENT_FUNCTION, __FILE__, __LINE__). This is true regardless of whether NDEBUG is defined.

    boost::assertion_failed is declared in <boost/assert.hpp> as

    namespace boost
{
    void assertion_failed(char const * expr, char const * function,
        char const * file, long line);
}

    but it is never defined. The user is expected to supply an appropriate definition.

  • If the macro BOOST_ENABLE_ASSERT_DEBUG_HANDLER is defined when <boost/assert.hpp> is included, BOOST_ASSERT(expr) expands to ((void)0) when NDEBUG is defined. Otherwise the behavior is as if BOOST_ENABLE_ASSERT_HANDLER has been defined.

As is the case with <cassert>, <boost/assert.hpp> can be included multiple times in a single translation unit. BOOST_ASSERT will be redefined each time as specified above.

BOOST_ASSERT_MSG

The macro BOOST_ASSERT_MSG is similar to BOOST_ASSERT, but it takes an additional argument, a character literal, supplying an error message.

  • By default, BOOST_ASSERT_MSG(expr,msg) expands to assert((expr)&&(msg)).

  • If the macro BOOST_DISABLE_ASSERTS is defined when <boost/assert.hpp> is included, BOOST_ASSERT_MSG(expr,msg) expands to ((void)0), regardless of whether the macro NDEBUG is defined.

  • If the macro BOOST_ENABLE_ASSERT_HANDLER is defined when <boost/assert.hpp> is included, BOOST_ASSERT_MSG(expr,msg) expands to

    (BOOST_LIKELY(!!(expr))? ((void)0): ::boost::assertion_failed_msg(#expr,
    msg, BOOST_CURRENT_FUNCTION, __FILE__, __LINE__))

    This is true regardless of whether NDEBUG is defined.

    boost::assertion_failed_msg is declared in <boost/assert.hpp> as

    namespace boost
{
    void assertion_failed_msg(char const * expr, char const * msg,
        char const * function, char const * file, long line);
}

    but it is never defined. The user is expected to supply an appropriate definition.

  • If the macro BOOST_ENABLE_ASSERT_DEBUG_HANDLER is defined when <boost/assert.hpp> is included, BOOST_ASSERT_MSG(expr) expands to ((void)0) when NDEBUG is defined. Otherwise the behavior is as if BOOST_ENABLE_ASSERT_HANDLER has been defined.

As is the case with <cassert>, <boost/assert.hpp> can be included multiple times in a single translation unit. BOOST_ASSERT_MSG will be redefined each time as specified above.

BOOST_VERIFY

The macro BOOST_VERIFY has the same behavior as BOOST_ASSERT, except that the expression that is passed to BOOST_VERIFY is always evaluated. This is useful when the asserted expression has desirable side effects; it can also help suppress warnings about unused variables when the only use of the variable is inside an assertion.

  • If the macro BOOST_DISABLE_ASSERTS is defined when <boost/assert.hpp> is included, BOOST_VERIFY(expr) expands to ((void)(expr)).

  • If the macro BOOST_ENABLE_ASSERT_HANDLER is defined when <boost/assert.hpp> is included, BOOST_VERIFY(expr) expands to BOOST_ASSERT(expr).

  • Otherwise, BOOST_VERIFY(expr) expands to ((void)(expr)) when NDEBUG is defined, to BOOST_ASSERT(expr) when it’s not.

BOOST_VERIFY_MSG

The macro BOOST_VERIFY_MSG is similar to BOOST_VERIFY, with an additional parameter, an error message.

  • If the macro BOOST_DISABLE_ASSERTS is defined when <boost/assert.hpp> is included, BOOST_VERIFY_MSG(expr,msg) expands to ((void)(expr)).

  • If the macro BOOST_ENABLE_ASSERT_HANDLER is defined when <boost/assert.hpp> is included, BOOST_VERIFY_MSG(expr,msg) expands to BOOST_ASSERT_MSG(expr,msg).

  • Otherwise, BOOST_VERIFY_MSG(expr,msg) expands to ((void)(expr)) when NDEBUG is defined, to BOOST_ASSERT_MSG(expr,msg) when it’s not.

BOOST_ASSERT_IS_VOID

The macro BOOST_ASSERT_IS_VOID is defined when BOOST_ASSERT and BOOST_ASSERT_MSG are expanded to ((void)0). Its purpose is to avoid compiling and potentially running code that is only intended to prepare data to be used in the assertion.

void MyContainer::erase(iterator i)
{
// Some sanity checks, data must be ordered
#ifndef BOOST_ASSERT_IS_VOID

    if(i != c.begin()) {
        iterator prev = i;
        --prev;
        BOOST_ASSERT(*prev < *i);
    }
    else if(i != c.end()) {
        iterator next = i;
        ++next;
        BOOST_ASSERT(*i < *next);
    }

#endif

    this->erase_impl(i);
}

  • By default, BOOST_ASSERT_IS_VOID is defined if NDEBUG is defined.

  • If the macro BOOST_DISABLE_ASSERTS is defined, BOOST_ASSERT_IS_VOID is always defined.

  • If the macro BOOST_ENABLE_ASSERT_HANDLER is defined, BOOST_ASSERT_IS_VOID is never defined.

  • If the macro BOOST_ENABLE_ASSERT_DEBUG_HANDLER is defined, then BOOST_ASSERT_IS_VOID is defined when NDEBUG is defined.