+
+
+ The predef_check utility provides
+ a facility for building a program that will check a given set of expressions
+ against the definitions it detected when it was built.
+
predef_check
+ programs
+
+ Even though there is only one predef_check
+ program, there are variations for each of the languages that are detected by
+ Predef to match the convention for sources files. For all of them one invokes
+ with a list of expression arguments. The expressions are evaluated within the
+ context of the particular predef_check program and if they
+ all are true zero (0) is returned. Otherwise the index of the first false expression
+ is returned.
+
+ The expression syntax is simple: +
+predef-definition [ relational-operator version-value ] ++
+ predef-definition can be any of the Predef definitions.
+ For example BOOST_COMP_GCC.
+
+ relational-operator can be any of: >,
+ <, >=, <=,
+ == and !=.
+
+ version-number can be a full or partial version
+ triplet value. If it's a partial version triple it is completed with zeros.
+ That is x.y is equivalent to x.y.0 and
+ x is equivalent to x.0.0.
+
+ The relations-operator and version-number
+ can be ommited. In which case it is equivalent to:
+
predef-definition > 0.0.0 ++
+ You can use the predef_check programs directly from Boost
+ Build to configure target requirements. This is useful for controlling what
+ gets built as part of your project based on the detailed version information
+ available in Predef. The basic use is simple:
+
import path-to-predef-src/check/predef + : check require + : predef-check predef-require ; + +exe my_windows_program : windows_source.cpp + : [ predef-require "BOOST_OS_WINDOWS" ] ; ++
+ That simple use case will skip building the my_windows_program
+ unless one is building for Windows. Like the direct predef_check
+ you can pass mutiple expressions using relational comparisons. For example:
+
import path-to-predef-src/check/predef + : check require + : predef-check predef-require ; + +lib my_special_lib : source.cpp + : [ predef-require "BOOST_OS_WINDOWS != 0" "BOOST_OS_VMS != 0"] ; ++
+ And in that case the my_special_lib is built only when the
+ OS is not Windows or VMS. The requires rule is a special
+ case of the check rule. And is defined in terms of it:
+
rule require ( expressions + : language ? )
+{
+ return [ check $(expressions) : $(language) : : <build>no ] ;
+}
+
+
+ You can use the check rule for more control and to implement
+ something other than control of what gets built. The definition for the check
+ rule is:
+
rule check ( expressions + : language ? : true-properties * : false-properties * ) ++
+ When invoked as a reuirement of a Boost Build target this rule will add the
+ true-properties to the target if all the expressions
+ evaluate to true. Otherwise the false-properties get added
+ as requirements. For example you could use it to enable or disable features
+ in your programs:
+
import path-to-predef-src/check/predef + : check require + : predef-check predef-require ; + +exe my_special_exe : source.cpp + : [ predef-check "BOOST_OS_WINDOWS == 0" + : <define>ENABLE_WMF=0 + : <define>ENABLE_WMF=1 ] ; ++
+ For both check and require the language
+ argument controls which variant of the predef_check program
+ is used to check the expressions. It defaults to "c++", but can be
+ any of: "c", "cpp", "objc", and "objcpp".
+
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