Question:
I'm having some trouble in declaring a STL Set of pointers to class instances. More specifically, I have this scenario:
class SimulatedDiskFile { private: // ... public: // ... struct comparator { bool operator () (SimulatedDiskFile* const& file_1, SimulatedDiskFile* const& file_2) { return ((*file_1)->getFileName() < (*file_2)->getFileName()); } }; } typedef set<SimulatedDiskFile*, SimulatedDiskFile::comparator> FileSet; The code above is not working. Compiler says it didn't find a member SimulatedDiskFile::comparator() function. If I put the function with this declaration (outside the struct), compiler says it was expecting a type.
Now here com my doubts (not only one, but related, I guess):
- What is the the correct declaration for a set of pointers?
- What is the correct declaration for a comparison funcion that compares pointers?
I did look up in many places before posting, but I found the references confusing and not quite related to my special case (as stupidly trivial as I think it is - actually, maybe this is the cause). So, any good links are of great help too!
Thanks in advance!
Solution:1
Fixing a few glitches,
#include <set> class SimulatedDiskFile { public: int getFileName() { return 23; } struct comparator { bool operator () (SimulatedDiskFile* file_1, SimulatedDiskFile* file_2) { return (file_1->getFileName() < file_2->getFileName()); } }; }; typedef std::set<SimulatedDiskFile*, SimulatedDiskFile::comparator> FileSet; compiles just fine.
Solution:2
Since you aren't showing where the 'getFileName()' method is supposed to be, I'm just going to go out on a limb and assume that you don't mean to double-dereference your pointers in the comparator. ie, you should do either:
return (file_1->getFileName() < file_2->getFileName()); or:
return ((*file_1).getFileName() < (*file_2).getFileName()); but not both.
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