Problem implemeting strcmp

I am trying to implement the strcmp function to be able to sort a list of businesses, but i keep getting an error on the line where it's supposed to be comparing them.

Code:

void business::Sort(vector<string>& list,string strcmp(const char *s1,const char *s2))
{
   if(list.size()==1){return;}
   else
   {
      for(int x=0;x<list.size();x++)
      {
         for(int y=0;y<list.size()-1;y++)
         {
            double b=(strcmp(list[y],list[y+1])); // error always happens here no matter how i try and change it
            if(b==-1)
            {swap(list[y],list[y+1]);}
         }
      }
   }
}

int business::strcmp(const char *s1, const char *s2)
{
while (*s1==*s2)
{
if(*s1=='\0')
return(0);
s1++;
s2++;
}
return(*s1-*s2);
}

Why do you need it? Why not just use std::string?

Looks like you're trying to pass a function pointer in to do the comparison. Yet the comparison function you want to use is already a member of the class. So, you can just call your strcmp in Sort(). Delete that parameter.

You have a number of problems here. First and biggest: You did not tell us *what* the error is.

Second, a string is not a const char*. If you really want to use your own c style strcmp function, you can get the c-string representation of an std::string with the member function c_str().

Why are you keeping the return value of strcmp as a double?

Why are you explicitly comparing the return value to -1? What if strcmp returns -2 or -3?