Một ví dụ về một địa chỉ IP với 24 bit trong mặt nạ được thể hiện trong hình . Octet đầu tiên (206) chỉ ra một loạt các loại C (Internet-giao) địa chỉ IP với t định dạng, với một mặt nạ nhị phân tiêu chuẩn chỉ . Điều này có nghĩa là chúng ta có 8 bit trong octet cuối cùng cho máy chủ. | strcpy p data_file In practice this code creates a string in system_file_name that is composed of path . So if for example the executable file is called and resides in the directoryborlandc then system_file_name will be assigned with borlandc . Returning from a Function The return command is used to return immediately from a function. If the function is declared with a return data type then return should be used with a parameter of the same data type. Function Prototypes Prototypes for functions allow the C compiler to check that the type of data being passed to and from functions is correct. This is very important to prevent data overflowing its allocated storage space into other variables areas. A function prototype is placed at the beginning of the program after any preprocessor commands such as include and before the declaration of any functions. C Preprocessor Commands In C commands to the compiler can be included in the source code. Called preprocessor commands they are defined by the ANSI standard to be if ifdef ifndef else elif endif include define undef line error pragma All preprocessor commands start with a hash or pound symbol and must be on a line on their own although comments may follow . These commands are defined in turn in the following subsections. define The define command specifies an identifier and a string that the compiler will substitute every time it comes across the identifier within that source code module. For example define FALSE 0 define TRUE FALSE The compiler will replace any subsequent occurrence of FALSE with 0 and any subsequent occurrence of TRUE with 0. The substitution does not take place if the compiler finds that the identifier is enclosed by quotation marks therefore 236 printf TRUE would not be replaced but printf d FALSE would be. The define command can also be used to define macros that may include parameters. The parameters are best enclosed in parentheses to ensure that correct .
