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Thinking in C++
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IntStack as a template

Here is the container and iterator from IntStack.cpp, implemented as a generic container class using templates:

//: C16:StackTemplate.h
// Simple stack template
#include "../require.h"

template<class T>
class StackTemplate {
  enum { ssize = 100 };
  T stack[ssize];
  int top;
  StackTemplate() : top(0) {}
  void push(const T& i) {
    require(top < ssize, "Too many push()es");
    stack[top++] = i;
  T pop() {
    require(top > 0, "Too many pop()s");
    return stack[--top];
  int size() { return top; }
#endif // STACKTEMPLATE_H ///:~

Notice that a template makes certain assumptions about the objects it is holding. For example, StackTemplate assumes there is some sort of assignment operation for T inside the push( ) function. You could say that a template “implies an interface” for the types it is capable of holding.

Another way to say this is that templates provide a kind of weak typing mechanism for C++, which is ordinarily a strongly-typed language. Instead of insisting that an object be of some exact type in order to be acceptable, weak typing requires only that the member functions that it wants to call are available for a particular object. Thus, weakly-typed code can be applied to any object that can accept those member function calls, and is thus much more flexible[63].

Here’s the revised example to test the template:

//: C16:StackTemplateTest.cpp
// Test simple stack template
//{L} fibonacci
#include "fibonacci.h"
#include "StackTemplate.h"
#include <iostream>
#include <fstream>
#include <string>
using namespace std;

int main() {
  StackTemplate<int> is;
  for(int i = 0; i < 20; i++)
  for(int k = 0; k < 20; k++)
    cout << is.pop() << endl;
  ifstream in("StackTemplateTest.cpp");
  assure(in, "StackTemplateTest.cpp");
  string line;
  StackTemplate<string> strings;
  while(getline(in, line))
  while(strings.size() > 0)
    cout << strings.pop() << endl;
} ///:~

The only difference is in the creation of is. Inside the template argument list you specify the type of object the stack and iterator should hold. To demonstrate the genericness of the template, a StackTemplate is also created to hold string. This is tested by reading in lines from the source-code file.

Thinking in C++
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   Reproduced courtesy of Bruce Eckel, MindView, Inc. Design by Interspire