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Visual C++ 2008 Feature Pack: MFC Enhancements

  • May 12, 2008
  • By Nick Wienholt
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Although the pace of managed language development appears to dwarf the rate of change in the C++ language, the development of new language features in C++ continues at the same measured pace that characterizes the language as a whole. Compared to languages such as Visual Basic that buckle and morph with each new trend, long-term stability is one of the C++ language's key features, and changes happen at a steadier pace and with greater scrutiny. Work is currently underway on additions to the C++ language currently referred to as the C++0x Standard, reflecting the expected ratification of the standard this decade. Technical Report 1 (TR1) is an interim step in this standardization process, and incorporates many of the new features that are likely to form part of the final standard.

In a previous article, the MFC Feature Pack and its installation was covered is some depth. These instructions and tips won't be repeated here.

STL Array

One of the most noticeable omissions in the current STL collection of containers is a fixed-length array. Even though there are plenty of work-arounds (C-style arrays, vector and third-party libraries), adding a fixed length array to the STL is a no-brainer in terms of collections that a typical C++ programmer would require. Using the new array collection is quite simple—the array length is nominated as a template parameter, and the collection behaves much like the STL vector collection:

#include <array>
#include <iostream>
#include <string>

std::tr1::array<int, 3> intArray = {4, 8, 10};

std::tr1::array<int, 3> intArray2 = {4, 8};
intArray2[2] = 10;

std::cout << ((intArray == intArray2)?
   std::string("Arrays are equal"):
   std::string("Arrays aren't equal")
);

std::cout << std::endl;

for (std::tr1::array<int, 3>::const_iterator it =
   intArray2.begin();
   it != intArray2.end();
   ++it) {
   std::cout << " " << *it;
}

There are a few noteworthy points in the code sample: The contents of an array can be fully or partially specified with initializers, and the compiler can check both the type and length of the initializer to ensure that the initializer is compatible with the array's definition. Operator == has also been overridden to allow a value-by-value comparison of each element in the array to be performed, and iterators works in exactly the same way as other STL collections. It is also worth noting that all the TR1 extensions that ship as part of the Visual C++ 2008 feature pack are contained in the std::tr1 namespace.

Regular Expressions

Although many third-party toolkits for executing regular expressions in C++ exist, they often fail to deliver the desired degree of integration with the Standard C++ library. By directly adding regular expressions to C++, it is possible to use the results of regular expression execution in the algorithms that form part of the STL, and to write code that will compile across a wide variety of compilers.

The regular expression library follows a similar pattern to the Standard C++ basic_string class—the most important class in the TR1 regular expression library is basic_regex, which wraps a regular expression, and a template parameter of basic_regex that specifies whether char or wchar characters will be used. As with basic_string, a typedef is pre-defined for the char and wchar basic_regex varieties. The basic_regex class is typically constructed with the regular expression string and any flags that specify behavior such as case-sensitivity and the regular expression language to use (basic, extended, ECMAScript, awk, grep, and egrep are all supported), and the regular expression object is then passed with a target string to one of the regular expression template functions.

Three template functions are available: regex_match, regex_search and regex_replace. The regex_match template function is used to determine whether a target string matches the basic_regex object passed in. regex_search determines whether the regular expression matches any text in the target string and can optionally populate a match_results object that will contain the regular expression capture groups. The final template function is regex_replace, which is used to do string replacements based on the results of the regular expression's execution.

This code sample shows the execution of a very simple email validation regular expression against two string constants (the point of the example is not the regular expression, which is overly simple for real email validation). The example prints whether the regular expression matches the target string.

#include <regex>
#include <iostream>
#include <string>

basic_regex<char> regex("[A-Z0-9._%+-]+@[A-Z0-9.-]+\\.[A-Z]{2,4}",
                        basic_regex<char>::icase);

cout<< std::boolalpha  << regex_match("GoOD@DOMAIN.COM", regex)
    << std::endl;

cout<< std::boolalpha  << regex_match("@DOMAIN.COM", regex)
    << std::endl;

Function Objects

Function objects will be familiar to C++/CLI developers who have previously used delegates—function objects offer type-safe function pointers that also can contain additional data that needs to be accessed as part of the functions execution. In contrast to raw function pointers that are not type-safe, the TR1 function template allows a function to be defined in terms of its return type and parameters, and for functions that meet this signature to be instantiated as part of the template instance and called without the need for a cast. The code below shows the use of a function object to call a function.

bool PrintData(int i, double d){
   cout << i;
   cout << endl;
   cout << scientific << d;
   cout << endl;

   return true;
}

{
   function<bool (int, double)> myPrint(PrintData);
   bool res = myPrint(1, 2.0);
}

The obvious benefit of function objects is the lack of casting required. The myPrint object can call the PrintData function without the need for a messy and potentially dangerous cast to a function point.





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