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< title > The MPL Reference Manual: BOOST_MPL_ASSERT_MSG</ title >
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< td class = "header-group page-location" >< a href = "../refmanual.html" class = "navigation-link" > Front Page</ a > / < a href = "./macros.html" class = "navigation-link" > Macros</ a > / < a href = "./asserts.html" class = "navigation-link" > Asserts</ a > / < a href = "./assert-msg.html" class = "navigation-link" > BOOST_MPL_ASSERT_MSG</ a ></ td >
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< div class = "section" id = "boost-mpl-assert-msg" >
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< h1 >< a class = "toc-backref" href = "./asserts.html#id1589" > BOOST_MPL_ASSERT_MSG</ a ></ h1 >
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< div class = "section" id = "id1294" >
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< h3 >< a class = "subsection-title" href = "#synopsis" name = "synopsis" > Synopsis</ a ></ h3 >
< pre class = "literal-block" >
#define < a href = "./assert-msg.html" class = "identifier" > BOOST_MPL_ASSERT_MSG</ a > ( condition, message, types ) \
< em > unspecified token sequence</ em > \
/**/
</ pre >
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< div class = "section" id = "id1295" >
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< h3 >< a class = "subsection-title" href = "#description" name = "description" > Description</ a ></ h3 >
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< p > Generates a compilation error with an embedded custom message when the condition
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doesn't hold.</ p >
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< div class = "section" id = "id1296" >
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< h3 >< a class = "subsection-title" href = "#header" name = "header" > Header</ a ></ h3 >
< pre class = "literal-block" >
#include < < a href = "../../../../boost/mpl/assert.hpp" class = "header" > boost/mpl/assert.hpp</ a > >
</ pre >
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< div class = "section" id = "id1297" >
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< h3 >< a class = "subsection-title" href = "#parameters" name = "parameters" > Parameters</ a ></ h3 >
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< table border = "1" class = "docutils table" >
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< colgroup >
< col width = "15%" />
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< thead valign = "bottom" >
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< tr >< th class = "head" > Parameter</ th >
< th class = "head" > Requirement</ th >
< th class = "head" > Description</ th >
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</ tr >
</ thead >
< tbody valign = "top" >
< tr >< td >< tt class = "literal" >< span class = "pre" > condition</ span ></ tt ></ td >
< td > An integral constant expression</ td >
< td > A condition to be asserted.</ td >
</ tr >
< tr >< td >< tt class = "literal" >< span class = "pre" > message</ span ></ tt ></ td >
< td > A legal identifier token</ td >
< td > A custom message in a form of a legal C++
identifier token.</ td >
</ tr >
< tr >< td >< tt class = "literal" >< span class = "pre" > types</ span ></ tt ></ td >
< td > A legal function parameter list</ td >
< td > A parenthized list of types to be displayed
in the error message.</ td >
</ tr >
</ tbody >
</ table >
</ div >
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< div class = "section" id = "id1298" >
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< h3 >< a class = "subsection-title" href = "#expression-semantics" name = "expression-semantics" > Expression semantics</ a ></ h3 >
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< p > For any integral constant expression < tt class = "literal" >< span class = "pre" > expr</ span ></ tt > , legal C++ identifier < tt class = "literal" >< span class = "pre" > message</ span ></ tt > , and
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arbitrary types < tt class = "literal" >< span class = "pre" > t1</ span ></ tt > , < tt class = "literal" >< span class = "pre" > t2</ span ></ tt > ,... < tt class = "literal" >< span class = "pre" > tn</ span ></ tt > :</ p >
< pre class = "literal-block" >
< a href = "./assert-msg.html" class = "identifier" > BOOST_MPL_ASSERT_MSG</ a > ( expr, message, (t1, t2,... tn) );
</ pre >
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< table class = "docutils field-list" frame = "void" rules = "none" >
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< col class = "field-name" />
< col class = "field-body" />
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< tr class = "field" >< th class = "field-name" > Return type:</ th >< td class = "field-body" >< p class = "first" > None.</ p >
</ td >
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</ tr >
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< tr class = "field" >< th class = "field-name" > Precondition:</ th >< td class = "field-body" >< p class = "first" >< tt class = "literal" >< span class = "pre" > t1</ span ></ tt > , < tt class = "literal" >< span class = "pre" > t2</ span ></ tt > ,... < tt class = "literal" >< span class = "pre" > tn</ span ></ tt > are non-< tt class = "literal" >< span class = "pre" > void</ span ></ tt > .</ p >
</ td >
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</ tr >
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< tr class = "field" >< th class = "field-name" > Semantics:</ th >< td class = "field-body" >< p class = "first" > Generates a compilation error if < tt class = "literal" >< span class = "pre" > expr</ span > < span class = "pre" > !=</ span > < span class = "pre" > true</ span ></ tt > , otherwise
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has no effect.</ p >
< p > When possible within the compiler's diagnostic capabilities,
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the error message will include the < tt class = "literal" >< span class = "pre" > message</ span ></ tt > identifier and the parenthized
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list of < tt class = "literal" >< span class = "pre" > t1</ span ></ tt > , < tt class = "literal" >< span class = "pre" > t2</ span ></ tt > ,... < tt class = "literal" >< span class = "pre" > tn</ span ></ tt > types, and have a general form of:</ p >
< pre class = "last literal-block" >
< em > ...</ em > ************( < em > ...</ em > ::message )************)(t1, t2,... tn) < em > ...</ em >
</ pre >
</ td >
</ tr >
</ tbody >
</ table >
< pre class = "literal-block" >
< a href = "./assert-msg.html" class = "identifier" > BOOST_MPL_ASSERT_MSG</ a > ( expr, message, (types< t1, t2,... tn> ) );
</ pre >
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< table class = "docutils field-list" frame = "void" rules = "none" >
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< col class = "field-name" />
< col class = "field-body" />
< tbody valign = "top" >
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< tr class = "field" >< th class = "field-name" > Return type:</ th >< td class = "field-body" >< p class = "first" > None.</ p >
</ td >
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</ tr >
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< tr class = "field" >< th class = "field-name" > Precondition:</ th >< td class = "field-body" >< p class = "first" > None.</ p >
</ td >
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</ tr >
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< tr class = "field" >< th class = "field-name" > Semantics:</ th >< td class = "field-body" >< p class = "first" > Generates a compilation error if < tt class = "literal" >< span class = "pre" > expr</ span > < span class = "pre" > !=</ span > < span class = "pre" > true</ span ></ tt > , otherwise
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has no effect.</ p >
< p > When possible within the compiler's diagnostics capabilities,
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the error message will include the < tt class = "literal" >< span class = "pre" > message</ span ></ tt > identifier and the list of
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< tt class = "literal" >< span class = "pre" > t1</ span ></ tt > , < tt class = "literal" >< span class = "pre" > t2</ span ></ tt > ,... < tt class = "literal" >< span class = "pre" > tn</ span ></ tt > types, and have a general form of:</ p >
< pre class = "last literal-block" >
< em > ...</ em > ************( < em > ...</ em > ::message )************)(types< t1, t2,... tn> ) < em > ...</ em >
</ pre >
</ td >
</ tr >
</ tbody >
</ table >
</ div >
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< div class = "section" id = "id1299" >
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< h3 >< a class = "subsection-title" href = "#example" name = "example" > Example</ a ></ h3 >
< pre class = "literal-block" >
template< typename T > struct my
{
// ...
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< a href = "./assert-msg.html" class = "identifier" > BOOST_MPL_ASSERT_MSG</ a > (
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is_integral< T> ::value
, NON_INTEGRAL_TYPES_ARE_NOT_ALLOWED
, (T)
);
};
my< void*> test;
// In instantiation of `my< void*> ':
// instantiated from here
// conversion from `
// mpl_::failed************(my< void*> ::
// NON_INTEGRAL_TYPES_ARE_NOT_ALLOWED::************)(void*)
// ' to non-scalar type `mpl_::assert< false> ' requested
</ pre >
</ div >
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< div class = "section" id = "id1300" >
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< h3 >< a class = "subsection-title" href = "#see-also" name = "see-also" > See also</ a ></ h3 >
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< p >< a class = "reference internal" href = "./asserts.html" > Asserts</ a > , < a class = "reference internal" href = "./assert.html" > BOOST_MPL_ASSERT</ a > , < a class = "reference internal" href = "./assert-not.html" > BOOST_MPL_ASSERT_NOT</ a > , < a class = "reference internal" href = "./assert-relation.html" > BOOST_MPL_ASSERT_RELATION</ a ></ p >
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<!-- Macros/Asserts//BOOST_MPL_ASSERT_NOT -->
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< td >< div class = "copyright-footer" >< div class = "copyright" > Copyright © 2001-2009 Aleksey Gurtovoy and David Abrahams</ div >
Distributed under the Boost Software License, Version 1.0. (See accompanying
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