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< title > BOOST_PP_FOR</ title >
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The < b > BOOST_PP_FOR</ b > macro represents a generalized horizontal repetition construct.
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< h4 > Usage</ h4 >
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< b > BOOST_PP_FOR</ b > (< i > state</ i > , < i > pred</ i > , < i > op</ i > , < i > macro</ i > )
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< h4 > Arguments</ h4 >
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< dt > state</ dt >
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The initial state.
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< dt > pred</ dt >
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A binary predicate of the form < i > pred</ i > (< i > r</ i > , < i > state</ i > ).
This macro must expand to an integer in the range of < i > 0</ i > to < b > BOOST_PP_LIMIT_MAG</ b > .
< b > BOOST_PP_FOR</ b > repeatedly expands < i > macro</ i > while this predicate returns non-zero.
This macro is called with the next available < b > BOOST_PP_FOR</ b > repetition and the current < i > state</ i > .
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< dt > op</ dt >
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A binary operation of the form < i > op</ i > (< i > r</ i > , < i > state</ i > ).
This operation is expanded by < b > BOOST_PP_FOR</ b > with the next available < b > BOOST_PP_FOR</ b > repetition and the current < i > state</ i > .
This macro is repeatedly applied to the < i > state</ i > , each time producing a new < i > state</ i > , until < i > pred</ i > returns < i > 0</ i > .
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< dt > macro</ dt >
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A binary macro of the form < i > macro</ i > (< i > r</ i > , < i > state</ i > ).
This macro is expanded by < b > BOOST_PP_FOR</ b > with the next available < b > BOOST_PP_FOR</ b > repetition and the current < i > state</ i > .
This macro is is repeated by < b > BOOST_PP_FOR</ b > until < i > pred</ i > returns < i > 0</ i > .
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< h4 > Remarks</ h4 >
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This macro expands to the sequence:
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< i > macro</ i > (< i > r</ i > , < i > state</ i > ) < i > macro</ i > (< i > r</ i > , < i > op</ i > (< i > r</ i > , < i > state</ i > )) ... < i > macro</ i > (< i > r</ i > , < i > op</ i > (< i > r</ i > , ... < i > op</ i > (< i > r</ i > , < i > state</ i > ) ... ))
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The < i > r</ i > value that is passed to < i > pred</ i > , < i > op</ i > , and < i > macro</ i > represents the next available < b > BOOST_PP_FOR</ b > repetition.
Other macros that have < b > _R</ b > suffix variants internally use < b > BOOST_PP_FOR</ b > --for example, < b > BOOST_PP_LIST_FOR_EACH</ b > and < b > BOOST_PP_LIST_FOR_EACH_R</ b > .
Using these < b > _R</ b > versions is not strictly necessary, but passing the < i > r</ i > value (that is passed to < i > pred</ i > , < i > op</ i > , and < i > macro</ i > ) to these macros allows them to reenter < b > BOOST_PP_FOR</ b > with maximum efficiency.
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To directly use this < i > r</ i > value, rather than simply passing it to another macro, see < b > BOOST_PP_FOR_< i > r</ i ></ b > .
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Previously, this macro could not be used recursively inside < b > BOOST_PP_FOR</ b > .
This limitation no longer exists, as the library can automatically detect the next available < b > BOOST_PP_FOR</ b > repetition.
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< h4 > See Also</ h4 >
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< li >< a href = "for_r.html" > BOOST_PP_FOR_< i > r</ i ></ a ></ li >
< li >< a href = "limit_mag.html" > BOOST_PP_LIMIT_MAG</ a ></ li >
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< h4 > Requirements</ h4 >
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< b > Header:</ b > < a href = "../headers/repetition/for.html" > < boost/preprocessor/repetition/for.hpp> </ a >
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< h4 > Sample Code</ h4 >
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#include < < a href = "../headers/arithmetic/inc.html" > boost/preprocessor/arithmetic/inc.hpp</ a > >
#include < < a href = "../headers/comparison/not_equal.html" > boost/preprocessor/comparison/not_equal.hpp</ a > >
#include < < a href = "../headers/repetition/for.html" > boost/preprocessor/repetition/for.hpp</ a > >
#include < < a href = "../headers/tuple/elem.html" > boost/preprocessor/tuple/elem.hpp</ a > >
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#define PRED(r, state) \
< a href = "not_equal.html" > BOOST_PP_NOT_EQUAL</ a > ( \
< a href = "tuple_elem.html" > BOOST_PP_TUPLE_ELEM</ a > (2, 0, state), \
< a href = "inc.html" > BOOST_PP_INC</ a > (< a href = "tuple_elem.html" > BOOST_PP_TUPLE_ELEM</ a > (2, 1, state)) \
) \
/**/
#define OP(r, state) \
( \
< a href = "inc.html" > BOOST_PP_INC</ a > (< a href = "tuple_elem.html" > BOOST_PP_TUPLE_ELEM</ a > (2, 0, state)), \
< a href = "tuple_elem.html" > BOOST_PP_TUPLE_ELEM</ a > (2, 1, state) \
) \
/**/
#define MACRO(r, state) < a href = "tuple_elem.html" > BOOST_PP_TUPLE_ELEM</ a > (2, 0, state)
< a href = "for.html" > BOOST_PP_FOR</ a > ((5, 10), PRED, OP, MACRO) // expands to 5 6 7 8 9 10
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< i > © Copyright < a href = "http://www.housemarque.com" target = "_top" > Housemarque Oy</ a > 2002</ i >
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</ br >< i > © Copyright Paul Mensonides 2002</ i >
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< p >< small > Distributed under the Boost Software License, Version 1.0. (See
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accompanying file < a href = "../../../../LICENSE_1_0.txt" > LICENSE_1_0.txt</ a > or
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copy at < a href =
"http://www.boost.org/LICENSE_1_0.txt" > www.boost.org/LICENSE_1_0.txt</ a > )</ small ></ p >
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