Understanding C++ Program Structure . This sample chapter covers function definitions, inline functions, recursion, pointers to functions, and functions with default arguments. It also describes structures and unions, member functions, and passing structures and unions as arguments. Additionally, you'll learn about C++ storage classes, exceptions, namespaces, and free store memory. This chapter is from the book . We begin with function definitions, inline functions, recursion. To organize data. We also look at C++ storage classes, exceptions, and namespaces. We do this to. encapsulate actions that functions perform. Encapsulation is important because. The first format is a function declaration. A comma- separated list. In a signature, each. Type may be distinct or the same as another one, and a function's. How to Declare Union in C? Union is similar to that of Structure. Syntax of both are same but major difference between structure and union is . In structures, each member has its own storage location. Structures and Unions. A structure can be considered as a template. Notice that in the above program the value 'Sam' is. Difference between a Structure and a Union in C. The below mentioned program gives a deep dive into structure and union. To get an idea of the usefulness of union. The c/c standard library defines no function. Learn how C++ program structure works, from the perspective of functions and data. C Program to Calculate Size of Structure using Sizeof Operator; C program to Use structure within union & display the contents of structure elements. Unions are conceptually similar to structures. The syntax of union is also similar to that of structure. The only differences is in terms of storage. In structure each member has its own storage location. C# / C Sharp Forums on Bytes. Type may be void or any built- in or user- defined type. Function prototypes must always precede function. Function signatures specify unique functions, much like handwriting. Here are several examples of function. The. argument names following their data types (p and q, for. Function prototypes with no. NOTEEarlier versions of C++ allowed an . Implicit int is no longer allowed (for function. Use void for functions that do. The second format is a function definition. The rest of the definition (function body) is a. Signatures that are not. The scope of an. argument (where it's valid) is inside the body of a function. Any C++. statement or construct is legal within the body of a function except another. NOTEIn files where you place function definitions before function calls, function. Be aware of forward referencing problems, however, as. Moving the function. In this. situation, a function prototype for f() or g() is necessary. Here's the function definition for area(), whose prototype. The formats for return. A return statement by itself appears only in functions whose return. The parentheses are optional in return. The formats are int main() . The second format handles programs with character string command- line. The second format makes each argument and the total number of. The variable argc is an. The variable argv is a. Each pointer in the array points. The first pointer, which is argv. This arrangement prevents accidental modifications to. Suppose, for example, we execute a C++ program called com, as. The second word is - r (presumably a program. The third command- line word is a file name called file. The last element of this. We use argv to access both characters and words from the command. Listing 3. 1. shows. Listing 3. 1 Command- line arguments // com. C - command- line arguments. If not, we use cerr to display a usage. NOTEAlways use argv. Lurleen Fischer author of Structures And Unions is from. Related Articles and Code: Program to illustrate the relationship b/w union and structure. Other Interesting Articles in C Programming: Program that displays use. Unions in C - Learn ANSI, GNU. C - Unions; C - Bit Fields; C - Typedef; C. The union statement defines a new data type. Learn how to create and use structs in C to create data structures. When a union is declared the compiler allocates enough memory for the largest data-type in the union. This ensures that. The notation argv. We return 0 (normal status) at the end of the program. NOTEThe Basic Rule (page 4. Referencing a character from a command- line word is a character. This two- dimensional array notation for argv is useful. The prototype for atof(), an. ASCII- to- float library routine, appears in the standard header file. Calls to function f() pass a floating point value. Inside. f(), we return a float that's two greater than the. We then use an assignment statement in the main program. Function g(), on the other hand, modifies. Note that a function prototype may appear inside or outside. Now consider what happens when we add the. We pass this integer value to. C++ conversion rules allow int- to- float conversions, and vice. Conversion rules, however, do not apply to pointers. Hence, the compiler. NOTEPlace your function prototypes in header files (. This. centralizes the interface for all modules that call your functions and makes it. Inline Functions. C++ functions typically use a run- time stack to push arguments and return. Programs that call functions repeatedly may therefore perform slowly. In. these situations, the keyword inline can make function calls execute. The formats are inline Type function. Inline functions, therefore, eliminate the code to push arguments and. A program's performance improves (no. Chapter 2 introduces macros that eliminate function call overhead with. Macros, however, are. Inline functions, on the other hand, give you the type safety of. The compiler performs type checking. Furthermore, pointers to inline functions are legal. None of. these features apply to macros. Macros also have problems that do not apply to inline functions. To. illustrate, let's contrast an inline function with a macro. The following. MAX macro, for instance, determines a maximum from its two arguments. The preprocessor output after textual. In general, we can't use operators ++ or - - with. Now let's convert MAX to an inline function for integers called. We pass the value of. Side effects are not the only problem with macros. Pointer arguments, for. MAX, and the result may not be what you. Inline function max(), on the other hand, generates compilation. NOTESpecifying inline is only a request to make a function inline. If. the body of an inline function is large or contains loops, your compiler may. For this reason, you. Profiling your application should identify which functions are. Although we were successful in rewriting macro MAX as an inline. The cout statement correctly displays 5, the number. Now let's convert the NELEMS. When you. pass the name of an array as an argument to a function, the compiler uses a. Therefore. nelems() divides the size of a pointer by the size of the first element. Judicious use of inline functions can make C++ programs. NOTEPlace inline function definitions (with function code statements) in header. Inline function definitions that appear in separate. Recursive Functions. C++ functions may call themselves. Depending on the algorithm, recursive. Recursive functions, on the other hand, use the. Suppose, for example, we need to write a function to convert integers to. Listing 3. 3 is a program that calls a. Listing 3. 3 Recursive integer- to- hexadecimal conversion // itoh. C - recursive integer- to- hex conversion. Otherwise, a cerr statement. The algorithm for the recursive. Each time. itoh() calls itself, the run- time stack allocates new memory locations. Recursion continues until the division. At this point, the run- time stack . The algorithm. uses the remainder from a modulus operation (%) as an offset into a. ASCII characters '0' to '9' and. The itoh() function is short and simple because the recursive design. Nonrecursive solutions are possible but not. Exercise 1 on page 1. NOTECan recursive functions be inline? Consider inlining the following. Most compilers inline only the first. Avoid inlining recursive functions and watch out for infinite. Pointers to Functions. C++ pointers may point to your own functions or library functions. Pointers. to functions are different than other pointer types because the addresses they. The. format for a pointer to a function is Type (*pfname)(Type arg. Type arg. 2, Type arg. N); where pfname is a pointer to a function whose signature is (Type. Type arg. 2, Type arg. N) and whose return type is Type. We need. the parentheses surrounding the indirection operator and pointer. Type. Figure 3. 2 shows an example of a. Figure. several examples. We cannot, however, assign help()'s address to. NOTEWhen you assign a function's address to a pointer, don't use. Parentheses following function. You may initialize a function pointer on the same line as the function. There are two ways to call functions with initialized function pointers. In the second format, the compiler calls the. To illustrate. suppose you want to call game() with a function pointer q. With a dispatch table, an index or simple lookup. The following program uses a. For simplicity. we restrict each table entry to a pointer to a math function that takes one. Listing 3. 4 Dispatch table // calc. C - dispatch table for math functions. NELEMS(A) (sizeof(A) / sizeof A. Here is the rest of the program, which accesses the dispatch. Listing 3. 5 Main program with dispatch table int main(int argc, const char *argv? If we do not find a function name from the command line that. Otherwise, we break from the. The statement cout < < mtab. Here are some. sample runs. The following. typedef definition, for example, eliminates the signature and pointer. Consider the following. A technique called the Right- Left. Rule. 1< span class=. In C++, a declaration may. To parse such. declarations, the compiler has to sort out the attributes listed in Table. Table 3. 1. Attributes. Attribute. Meaning()function. This means the declarations in Table 3. Table 3. 2. Legal attribute combinations. Attributes. Meaning*()function returns pointer(*)()pointer to function*. Illegal attribute combinations. Attributes. Meaning(). Otherwise, you're. Table 3. 3, such as an array of functions or a. Table 3. 4 lists the English keywords for the attributes, followed by the. Right- Left Rule. Table 3. 4. Attributes and Keywords. Attribute. English Keyword()function returns. Let's try it with some simple definitions first. Look to the right for. We stop at the data type (unsigned long). In the second example. Look to the right for the . This means p is an array of 2. Remember that multidimensional arrays use the . Here, ps is an array of 3. This, of course, is better. Now let's try a more complicated declaration. Looking right, we find that pa is an. Looking left, we see that it's an array of pointers. Looking right. we discover each array element is the address of a function that returns an. This means pa is an array of 5 pointers to functions that. NOTEThe parenthesis between the . Looking right, we know that g is a. Looking left, we see that this function returns a pointer. Looking. right, we find that the function returns a pointer to an array. Looking left. once more, we discover that each array element is a pointer to type. Therefore, g is a function that returns a pointer to an. Again, note that the parentheses. See if you agree with the following steps for an array of 1. Start with the name of the array. Instead of passing entire arrays to functions (which is inefficient). You cannot, therefore, pass arrays by.
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