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3dcgmodeling

count_if not work,why?

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struct cntor { cntor(){}; bool operator()() { return 1; } }; bool cnt(int i , int ii) { return 1; } void f() { int t[] = {3,4,5,6,7,8,9}; set<int> object_set(t,t+sizeof(t)/sizeof(int)); int cnt = count_if(t,t+sizeof(t)/sizeof(int),cntor()); //can not compile here. }

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If you could place your code in [ code ] [ /code ] or [ source ] [ /source ] tags but you'll need to remove the spaces it will make your code formatting a lot nicer.

The error results from you defining a function "bool cnt(int i, int ii);" but you also define a variable "int cnt" as well. Make sure the names are different and it should compile.

like

bool countFunc(int i, int ii)
{
return 1;
}
void f()
{
int t[] = {3,4,5,6,7,8,9};
set<int> object_set(t,t+sizeof(t)/sizeof(int));
int cnt = count_if(t,t+sizeof(t)/sizeof(int),cntor());
}


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The operator() for the cntor struct needs to accept a parameter. In this case the type would be 'int', because that's the type of the elements that are being iterated over. count_if will pass the elements of the array to the cntor instance, one at a time.

Also, please note that the bool type also supports literals 'true' and 'false', which you should use rather than 0 and 1. Further, std::set is already able to tell you how many elements it contains (and doesn't have to recount them every time; it stores the count separately), via .size().

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