【正文】 C and Database Development 一、 The Introduce of C In one sense, C can be seen as being the same thing to programming languages as .NET is to the Windows environment. Just as Microsoft has been adding more and more features to Windows and the Windows API over the past decade, Visual Basic and C++ have undergone expansion. Although Visual Basic and C++ have ended up as hugely powerful languages as a result of this, both languages also suffer from problems due to the legacies of how they have evolved. In the case of Visual Basic 6 and earlier, the main strength of the language was the fact that it was simple to understand and didn’t make many programming tasks easy, largely hiding the details of the Windows API and the COM ponent infrastructure from the developer. The downside to this was that Visual Basic was never truly objectoriented, so that large applications quickly bee disanized and hard to maintain. As well as this, because Visual Basic’s syntax was inherited from early versions of BASIC (which, in turn, was designed to be intuitively simple for beginning programmers to understand, rather than to write large mercial applications), it didn’t really lend itself to wellstructured or objectoriented programs. C++, on the other hand, has its roots in the ANSI C++ language definition. It isn’t pletely ANSIpliant for the simple reason that Microsoft first wrote its C++ piler before the ANSI definition had bee official, but it es close. Unfortunately, this has led to two problems. First, ANSI C++ has its roots in a decadeold state of technology, and this shows up in a lack of support for modern concepts (such as Unicode strings and generating XML documentation), and in some archaic syntax structures designed for the pilers of yesteryear (such as the separation of declaration from definition of member functions). Second, Microsoft has been simultaneously trying to evolve C++ into a language that is designed for highperformance tasks on Windows, and in order to achieve that they’ve been forced to add a huge number of Microsoftspecific keywords as well as various libraries to the language. The result is that on Windows, the language has bee a plete mess. Just ask C++ developers how many definitions for a string they can think of: char*, LPTSTR, string, CString (MFC version), CString (WTL version), wchar_t*, OLECHAR*, and so on. Now enter .NET—a pletely new environment that is going to involve new extensions to both languages. Microsoft has gotten around this by adding yet more Microsoftspecific keywords to C++, and by pletely revamping Visual Basic into Visual Basic .NET, a language that retains some of the basic VB syntax but that is so different in design that we can consider it to be, for all practical purposes, a new language. It’s in this context that Microsoft has decided to give developers an alternative—a language designed specifically for .NET, and designed with a clean slate. Visual C .NET is the result. Officially, Microsoft describes C as a “simple, modern, objectoriented, and typesafe programming language derived from C and C++.” Most independent observers would probably change that to “derived from C, C++, and Java.” Such descriptions are technically accurate but do little to convey the beauty or elegance of the language. Syntactically, C is very similar to both C++ and Java, to such an extent that many keywords are the same, and C also shares the same block structure with braces ({}) to mark blocks of code, and semicolons to separate statements. The first impression of a piece of C code is that it looks quite like C++ or Java code. Behind that initial similarity, however, C is a lot easier to learn than C++, and of parable difficulty to Java. Its design is more in tune with modern developer tools than both of those other languages, and it has been designed to give us, simultaneously, the ease of use of Visual Basic, and the highperformance, lowlevel memory access of C++ if required. Some of the features of C are: ? Full support for classes and objectoriented programming, including both interface and implementation inheritance, virtual functions, and operator overloading. ? A consistent and welldefined set of basic types. ? Builtin support for automatic generation of XML documentation. ? Automatic cleanup of dynamically allocated memory. ? The facility to mark classes or methods with userdefined attributes. This can be useful for documentation and can have some effects on pilation (for example, marking methods to be piled only in debug builds). ? Full access to the .NET base class library, as well as easy access to the Windows API (if you really need it, which won’t be all that often). ? Pointers and direct memory access are available if required, but the language has been designed in such a way that you can work without them in almost all cases. ? Support for properties and events in the style of Visual Basic. ? Just by changing the piler options, you can pile either to an executable or to a library of .NET ponents that can be called up by other code in the same way as ActiveX controls (COM ponents). ? C can be used to write dynamic Web pages and XMLWeb services. Most of the above statements, it should be pointed out, do also apply to Visual Basic .NET and Managed C++. The fact that C is designed from the start to work with .NET, however, means that its support for the features of .NET is both more plete, and offered within the context of a more suitable syntax than for those other languages. While the C language itself is very similar to Java, there are some improvements: in particular, Java is not designed to work with the .NET environment. Before we leave the subject, we should point out a couple of limitations of C. The one area the language is