CODEWITHSUNDEEP
c++templatesoop
highBandWidth
highBandWidth

Reputation: 17306

Need to have empty string as a template parameter

I want to have a class that stores a pair of variables of different types, but I need to pass the zero or null defaults for the variables as template parameters. I can do so for int or doubles, but how do I do so for string? I know that that c++ currently does not have string parameters, but what are the laternative designs. I need something like this:

#include <iostream>
#include <string>

using namespace std;

template <typename atype, typename btype, atype anull, btype bnull>
class simpleClass {
public:
    atype       var1;
    btype       var2;

    simpleClass<atype, btype, anull, bnull>   *parent;          // pointer to parent node

    simpleClass(); ~simpleClass();
};
template <typename atype, typename btype, atype anull, btype bnull>
simpleClass<atype, btype, anull, bnull>::simpleClass()  {   var1 = anull; var2 = bnull; 
                        parent  = NULL;  }
template <typename atype, typename btype, atype anull, btype bnull>
simpleClass<atype, btype, anull, bnull>::~simpleClass() {}


int main() {
    simpleClass<string, int, "", 0> obj;
    obj.var1 = "hello";
    obj.var2 = 45;
    cout << obj.var2;
    return 0;
}

compiling this, I get

error: ‘struct std::string’ is not a valid type for a template constant parameter

Upvotes: 2

Views: 648

Answers (1)

Puppy
Puppy

Reputation: 146968

You cannot pass non-integral types as template parameters, except for pointers and references. The best behaviour you could hope for is to pass a function which returns a "default" value for atype and btype.

Upvotes: 4

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