my count_if() implementation doesnt work

etrusks (163)
Hi, I'm having trouble understanding 1 thing so here it is!

1. I created my count_if function
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template<class Iter, class Pred>
int count_if(Iter begin, Iter end, Pred pred){

    int sum = 0;

    for(; begin != end; ++begin){
        if(pred(*begin)) sum++;
    }

    return sum;
}


and than wrote simple predicate function
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template<class T>
bool bigger_than(T val){
    if(10 < val) return true;
    else return false;
}


The problem is that I'm getting this error

/home/girts/Desktop/exercises/chapter_21/exercise_4/main.cpp:40: error: no matching function for call to 'count_if(std::vector<int>::iterator, std::vector<int>::iterator, <unresolved overloaded function type>)'
     std::cout << count_if(vec.begin(), vec.end(), bigger_than) << std::endl;
                                                              ^


If I remove template stuff from my function than its running fine. Also works fine with function object.

Full code if someone wants to run it
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/* 4. Implement count_if() yourself! Test it !*/

#include <vector>
#include <iostream>

template<class Iter, class Pred>
int count_if(Iter begin, Iter end, Pred pred){

    int sum = 0;

    for(; begin != end; ++begin){
        if(pred(*begin)) sum++;
    }

    return sum;
}

template<class T>
bool bigger_than(T val){
    if(10 < val) return true;
    else return false;
}

struct biger{
    int val;

    biger(int v) : val{v}{}
    bool operator()(int V){
        if(val < V) return true;
        else return false;
    }
};

int main(){

    std::vector<int> vec {8, 12, 9, 5, 33, 4, 5,
                          4, 1, 20, 18, 17, 28, 1};

    //std::cout << count_if(vec.begin(), vec.end(), biger(10)) << std::endl;
    std::cout << count_if(vec.begin(), vec.end(), bigger_than) << std::endl;
}
Peter87 (6678)
You forgot to specify what instantiation of bigger_than you want to use.
 
 
std::cout << count_if(vec.begin(), vec.end(), bigger_than<int>) << std::endl;
Last edited on
andywestken (3890)
Try

std::cout << count_if(vec.begin(), vec.end(), bigger_than<int>) << std::endl;

for line 40.

Andy
etrusks (163)
Ohh, thanks guys so much :)
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