使用谓词模板函数从此处实例化错误

Question

I tried researching this question already, but it seems as though every question dealing with my error has to do with classes and their default constructors whereas my code contains no classes. It's a simple size() function that returns the number of elements in a given array. (I'm aware there is a built in size() function, that's not the point).

I at first thought that it was upset with my naming my function size() when a size() function already existed so I changed mine to sise() but I still recieve the same error and have no idea how to solve it.

Code:

template<class T > int sise(T array[], int count){
  if(array[count+1]== NULL){
    return count+1;
  }
  else{
    return sise(array,count+1);
  }
}

template <class T> int sise(T array[]){
  return sise(array , 0);
  }

int main(){
  int array[] = {1 , 7 , 5, 4, 6 ,2 , 3};
  int len = sise<int>(array);
  std::cout << len << std::endl;
  //print<int>(array);
  //  shakersort<int>(array);
  // print<int>(array);

  return 0;
}

Don't worry about the commented out function calls in main(), as each respective's calls functions have been commented out but the same error of

Shakersort.cpp: In function ‘int sise(T*, int) [with T = int]’:
Shakersort.cpp:60:24:   instantiated from ‘int sise(T*) [with T = int]’
Shakersort.cpp:77:28:   instantiated from here
Shakersort.cpp:51:3: warning: NULL used in arithmetic [-Wpointer-arith]

is given. What is going on?

Answer 1

The compiler is warning about NULL being compared to an int from the looks of it. Not strictly an error (nor is it made an error) but a likely indication of false assumptions being made. One such assumption seems to be that arrays are magically null-terminated: they are not. That is something very specific to string literals and even then the null-terminator is not NULL but rather '\\0' . You'll either need to pass the size of the array along or you'll need to deduce it using a template, eg:

template <typename T, int Size>
int sise(T (&array)[Size], int count) {
    ...
}