11.10 Using Templates Without the Standard Library

Several of the Tools.h++ templates, such as RWTValVector<T>, RWTPtrVector<T>, RWTIsvSlist<T>, and RWTIsvDlist<T>, are not based on the Standard C++ Library. You can use them on any of our certified platforms. Also, as mentioned previously in the Introduction, you can use many of the so-called standard library-based templates without the Standard C++ Library, as long as you keep to a subset of the full interface.

The restricted subset interfaces are almost fully upward compatible with their corresponding standard library-based interfaces. The major difference you will find is that some collections take a different number of template parameters, depending on which underlying implementation they are using. For example, when RWTPtrHashSet is used with the Standard C++ Library, it takes three template arguments as described in Section XX above. However, when that same class is used without the Standard C++ Library, the restricted interface calls for only one template parameter, namely the type of item being contained. To help you write portable code that works with or without the Standard C++ Library, Tools.h++ provides two macros:

1. Use the first macro, RWDefHArgs(T), standing for Rogue Wave Default Hash Arguments, for the hash-based template collections. For example, by declaring:

   RWTPtrHashSet<int RWDefHArgs(int)> hset;

   you declare a hash-based set that will have the same semantics whether or not the Standard C++ Library is present. Note that you should not use a comma between the element type and the macro. Without the Standard C++ Library, the macro expands to nothing and it is as if you had declared:

   RWTPtrHashSet<int> hset;

   However, as soon as the Standard C++ Library becomes available, the macro expands as follows:

   RWTPtrHashSet<int ,RWTHasher<int>, equal_to<int> > hset;

   This declaration satisfies the full requirement of the standard library-based interface for all three parameters, and keeps the semantics consistent with the alternative non standard-library based implementation.

2. The second macro, RWDefCArgs(T), is similar to the first. Standing for Rogue Wave Default Comparison Arguments, RWDefCArgs(T)is available for use with RWTPtrSortedVector and RWTValSortedVector. For example:

   RWTValSortedVector<int RWDefCArgs(int)> srtvec;

   is a portable declaration that will work with or without the Standard C++ Library. Again, do not use a comma to separate the element type from the macro.

Let's start with a simple example that uses RWTValVector<T>, one of the classes that is not based on the Standard C++ Library.

#include <rw/tvvector.h>                                   // 1

main() {
    RWTValVector<double> vec(20, 0.0);                     // 2

    int i;
    for (i=0; i<10; i++)     vec[i] = 1.0;                 // 3
    for (i=10; i<20; i++)    vec(i) = 2.0;                 // 4

    vec.reshape(30);                                       // 5
    for (i=20; i<30; i++)    vec[i] = 3.0;                 // 6
    return 0;
    }
 

Each program line is detailed below.

The second example involves a hashing dictionary. By using the macro RWDefHArgs(T) when you declare the hashing dictionary, you insure that your code is portable with or without access to the Standard C++ Library.

#include <rw/tvhdict.h>
#include <rw/cstring.h>
#include <rw/rstream.h>
#include <iomanip.h>

class Count {                                                  // 1
  int  N;
public:
  Count() :    N(0) { }                                        // 2
  int  operator++()  { return ++N; }                           // 3
  operator   int() { return N; }                               // 4
};

unsigned hashString ( const RWCString& str )                   // 5
  { return str.hash(); }

main() {

  RWTValHashDictionary<RWCString,
                       Count  /* Note: no comma here! */
                       RWDefHArgs(RWCString)> hmap(hashString); //6


  RWCString token;
  while ( cin >> token )                                       // 7
    ++hmap[token];                                             // 8

  RWTValHashDictionaryIterator<RWCString,Count> next(hmap);    // 9

  cout.setf(ios::left, ios::adjustfield);                     // 10
  while ( ++next )                                            // 11
    cout << setw(20) << next.key()
         << " " << setw(10) << next.value() << endl;          // 12

  return 0;
}
 

Program Input:
How much wood could a woodchuck chuck if a woodchuck could chuck wood ?

Program Output:
much                 1
wood                 2
a                    2
if                   1
woodchuck            2
could                2
chuck                2
How                  1
?                    1

In the code above, the problem is to read an input file, break it up into tokens separated by white space, count the number of occurrences of each token, and then print the results. The general approach is to use a dictionary to map each token to its respective count. Here's a line-by-line description: