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The most vexing parse is a specific form of syntactic ambiguity resolution in the C++ programming language. The term was used by Scott Meyers in ''Effective STL'' (2001). It is formally defined in section 8.2 of the C++ language standard.〔ISO/IEC (2003). ''ISO/IEC 14882:2003(E): Programming Languages - C++ §8.2 Ambiguity resolution ()''〕 == Example with classes == An example is: class Timer ; class TimeKeeper ; int main() The line TimeKeeper time_keeper(Timer()); is ambiguous, since it could be interpreted either as # a variable definition for variable of class , initialized with an anonymous instance of class or # a function declaration for a function which returns an object of type and has a single (unnamed) parameter which is a function returning type (and taking no input). (See Function object#In C and C++) Most programmers expect the first, but the C++ standard requires it to be interpreted as the second. For example, g++ gives the following error message: $ g++ -c time_keeper.cc time_keeper.cc: In function ‘int main()’: time_keeper.cc:15: error: request for member ‘get_time’ in ‘time_keeper’, which is of non-class type ‘TimeKeeper(Timer ( *)())’ Clang++ provides a warning: $ clang++ time_keeper.cc timekeeper.cc:14:25: parentheses were disambiguated as a function declaration () TimeKeeper time_keeper(Timer()); timekeeper.cc:14:26: note: add a pair of parentheses to declare a variable TimeKeeper time_keeper(Timer()); timekeeper.cc:15:21: member reference base type 'TimeKeeper (Timer ( *)())' is not a structure or union return time_keeper.get_time(); One way to force the compiler to consider this as a variable definition is to add an extra pair of parentheses: TimeKeeper time_keeper( (Timer()) ); 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Most vexing parse」の詳細全文を読む スポンサード リンク
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