template specialization : does not match any template declaration

c++, templates

Solution

You have explicitly specialized the class, resulting in a fully instantiated type called `chrrr<char>`. You don't need to give the template arguments when defining the member function. Simply:

char chrrr<char>::chgchr(char c){
    return c+2; 
}

However, it seems you are specializing the whole class just to specialize a single function. You can do that with:

template <class T>
class chrrr {
    public:
    T chgchr(T c);  
};

template <class T> 
T chrrr<T>::chgchr(T c){
    return c+1; 
}

// Explicitly specialize for the member function
template <>
char chrrr<char>::chgchr(char c){
    return c+2; 
}

Problem

When I study the template specialization, I use a very simple example, but I still got error. ``` #include <iostream> template <class T> class chrrr{ public: T chgchr(T c); }; template < class T> T chrrr<T>::chgchr(T c){ return c+1; } template <> class chrrr<char>{ public: char chgchr(char c); }; template <> char chrrr<char>::chgchr(char c){ return c+2; } using namespace std; int main(){ char a='a'; int i=1; chrrr<int> it; chrrr<char> ch; cout<<ch.chgchr(a)<<endl; cout<<it.chgchr(i)<<endl; return 0; } ``` The error said: ``` line 20: error: template-id ‘chgchr<>’ for ‘char chrrr<char>::chgchr(char)’ does not match any template declaration ``` I wonder why it dose not match? And if I define chgchr in class definition body rather than out side, it works very well.

Original source