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Compiler Error C2893

Failed to specialize function template 'template name'

The compiler failed to specialize a function template. There can be many causes for this error.

In general, the way to resolve a C2893 error is to review the function's signature and make sure you can instantiate every type.

C2893 occurs because f's template parameter T is deduced to be std::map<int,int>, but std::map<int,int> has no member data_type (T::data_type can not be instantiated with T = std::map<int,int>.). The following sample generates C2893.

// C2893.cpp
// compile with: /c /EHsc
#include<map>
using namespace std;
class MyClass {};

template<class T> 
inline typename T::data_type
// try the following line instead
// inline typename  T::mapped_type
f(T const& p1, MyClass const& p2);

template<class T>
void bar(T const& p1) {
    MyClass r;
    f(p1,r);   // C2893
}

int main() {
   map<int,int> m;
   bar(m);
}
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