C++ Templates with function declaration/ protype and definition

Question

I'm new to templates, was reading up on them and found a great video tutorial on them .

Furthermore, I know that there are two types of templates, class and function templates. However, in my snippet of code I only wanted to use a function template instead of a class template, but I wanted to have a function declaration and definition that makes use of the template. It seems a little weird to have the same code for the template in the function definition and declaration (I read a thread on this on the cpp website, but I can only post two links right now).

Is this the correct syntax for using a template with a function declaration and definition?

• A.

Here is the snippet of consolidated code:

class GetReadFile {
public:
    // Function Declaration
    template <size_t R, size_t C>   // Template same as definition
    bool writeHistory(double writeArray[R][C], string path);
};

// Function Definition
template <size_t R, size_t C>      // Template same as declaration
bool GetReadFile::writeHistory(double writeArray[R][C], string path){...}

Answer 1

If you're calling it the right way, the syntax works well for me:

GetReadFile grf;
double array[5][8];    
grf.writeHistory<5,8>(array,"blah");

See live demo .

Note though:
Simply calling that method without specifying the actual array dimensions, these can't be automatically deduced by the compiler:

grf.writeHistory(array,"blah");

Fails with

main.cpp:24:34: error: no matching function for call to 'GetReadFile::writeHistory(double [5][8], const char [5])'  
  grf.writeHistory(array,"blah");
                              ^
  ...
main.cpp:10:10: note:   template argument deduction/substitution failed:
main.cpp:24:34: note:   couldn't deduce template parameter 'R'
 grf.writeHistory(array,"blah");

See the alternate demo .