templated classes with friend functions

[Orphious]

I am trying to overload the >> operator in a templated class. Now normally, you could make a friend function. But I have heard that friend functions in a templated class must be inlined. Is that true? If so, what would the syntax be. Something as simple as this?

template <typename T>
class test
{
private:
//data variables

public:
inline istream& operator >> (istream& stream, test& var);
};

Is my thinking correct on this. Cause I did try originally and make it a friend function but it didn't work. Got alot of errors about istream and >>. Thanks guys

[Orphious]

Say I have a string d ="-*abc";
and I want to loop through it, is there a way I can store the address location of d[i] via a pointer. Can I store it in a stack? I tried it but of course it didn't work.

stack<char*> temp; //couldnt it be a char pointer since d[i] is a char?
for (int i=0;i<d.length();i++)
{
char* var=d[i];
temp.push(var);
}

Any ideas?

[Stu]

First question, first part. I've had friends in templates without having them defined as inline without any problems, so I doubt it's a rule.

First question, second part. Remember that any member defined in the class declaration is, by default, inline. So:

template <typename T> 
class test {
 
private: 

  //data variables 

public:

  // The following method is inline... 
  istream& operator >> (istream& stream, test& var){

    // Do something and return it...

  } 

};

Therefore, if you want it to be a friend and inline, define it in the class--like so.

template <typename T> 
class test {
 
private: 

  //data variables 

public:

  // The following method is inline... 
  friend istream& operator >> (istream& stream, test& var){

    // Do something and return it...

  } 

};

Second question, a string is a type of container. So, you can use iterators. Like so:

#include <iostream>
#include <string>

int main(int argc, char **argv){

  string s("-*abc");    // String
  string::iterator it;  // Iterator for the string

  // Print one character per line...
  for (it = s.begin(); it != s.end(); it++)
    cout << *it << '\n' << ends;

  // Print empty line...
  cout << '\n' << ends;

  // Set the iterator to the first character...
  it = s.begin();

  // Move to the third character (two characters ahead)...
  it += 2;

  // Print the third character...
  cout << *it << '\n' << ends;

  return 0;

}  // End main()

[Orphious]

I understand that strings are containers and I can use iterators. But how could I use them if I wanted to keep track of the following in the string

string s("-*abc");

I'd want to keep track of chars - and * . I was thinking stack because if I want to run through again and look for - then do something like if (stack.top()==locationof-)
do something

How could I do something similiar if I don't know the string, I just want to keep track of all the operators

[Stu]

You just want the positions, or a iterator to the actual contents of the positions? For the former you could try something like this:

#include <iostream>
#include <string>
#include <vector>

int main(int argc, char **argv){

  string s("-*abc");                // String
  string ops("+-*/%");              // Operators
  vector<string::size_type> v_pos;  // Vector for the positions

  // Loop through and get the positions...
  for(string::size_type pos = 0;
      (pos = s.find_first_of(ops, pos)) != string::npos;
      pos++)
    v_pos.push_back(pos);

  // Print the results...
  for(vector<string::size_type>::iterator it = v_pos.begin();
      it != v_pos.end();
      it++)
    cout << "[ "
         << s[*it]
         << " ] found at position "
         << *it
         << '\n'
         << ends;

}  // End main()

For the latter, something like this should do the trick:

#include <iostream>
#include <string>
#include <vector>

int main(int argc, char **argv){

  string s("-*abc");                // String
  string ops("+-*/%");              // Operators
  vector<string::iterator> v_it;    // Vector for the iterators

  // Loop through and get the values as iterators...
  for(string::size_type pos = 0;
      (pos = s.find_first_of(ops, pos)) != string::npos;
      pos++){

    string::iterator temp_it = s.begin() + pos;

    v_it.push_back(temp_it);

  }  // End for

  // Print the results...
  for(vector<string::iterator>::iterator it = v_it.begin();
      it != v_it.end();
      it++)
    cout << "[ "
         << **it
         << " ] found at position "
         << *it - s.begin()
         << '\n'
         << ends;

}  // End main()

[Orphious]

I'll give these a shot!