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Thinking in C++
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What's wrong?

We are remarkably adaptable, even in situations in which perhaps we shouldn’t adapt. The style of the CStash library has been a staple for C programmers, but if you look at it for a while, you might notice that it’s rather . . . awkward. When you use it, you have to pass the address of the structure to every single function in the library. When reading the code, the mechanism of the library gets mixed with the meaning of the function calls, which is confusing when you’re trying to understand what’s going on.

One of the biggest obstacles, however, to using libraries in C is the problem of name clashes. C has a single name space for functions; that is, when the linker looks for a function name, it looks in a single master list. In addition, when the compiler is working on a translation unit, it can work only with a single function with a given name.

Now suppose you decide to buy two libraries from two different vendors, and each library has a structure that must be initialized and cleaned up. Both vendors decided that initialize( ) and cleanup( ) are good names. If you include both their header files in a single translation unit, what does the C compiler do? Fortunately, C gives you an error, telling you there’s a type mismatch in the two different argument lists of the declared functions. But even if you don’t include them in the same translation unit, the linker will still have problems. A good linker will detect that there’s a name clash, but some linkers take the first function name they find, by searching through the list of object files in the order you give them in the link list. (This can even be thought of as a feature because it allows you to replace a library function with your own version.)

In either event, you can’t use two C libraries that contain a function with the identical name. To solve this problem, C library vendors will often prepend a sequence of unique characters to the beginning of all their function names. So initialize( ) and cleanup( ) might become CStash_initialize( ) and CStash_cleanup( ). This is a logical thing to do because it “decorates” the name of the struct the function works on with the name of the function.

Now it’s time to take the first step toward creating classes in C++. Variable names inside a struct do not clash with global variable names. So why not take advantage of this for function names, when those functions operate on a particular struct? That is, why not make functions members of structs?

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