A First Book of ANSI C—ch14.pptVIP

Linux+ Guide to Linux Certification, Second Edition A First Book of ANSI C, Fourth Edition A First Book of ANSI CFourth Edition Chapter 14 Additional Capabilities Objectives Additional Features Bit Operations Macros Command-Line Arguments Common Programming and Compiler Errors Additional Features The typedef declaration statement Conditional preprocessor directives Enumerated constants Conditional expressions The goto statement The typedef Declaration Statement typedef permits constructing alternate names for an existing C data type name typedef double REAL; makes the REAL an alias for double REAL val; is equivalent to double val; typedef does not create a new data type The equivalence produced by typedef can frequently be produced equally well by #define typedef processed by the compiler #define processed by the preprocessor The typedef Declaration Statement (continued) Another example: typedef int ARRAY[100]; ARRAY first, second; Equivalent to the two definitions int first[100]; and int second[100]; As another example: typedef struct { char name[20]; int idNum; } empRecord; empRecord employee[75]; Conditional Preprocessor Directives #ifndef and #ifdef permit conditional compilation in that the statements immediately following these directives, up to an #else or #endif, are compiled only if the condition is true, whereas the statements following the #else are compiled only if the condition is false For example, #ifndef condition compile the statements placed here #else compile the statements placed here #endif Conditional Preprocessor Directives (continued) The #else directive is optional #ifndef is the most frequently used conditional preprocessor directive Its most common usage is in the form #ifndef header-file #include header-file #endif For example: #ifndef stdio.h #include stdio.h #endif Enumerated Constants Set of related integer values can be equated to an equivalent set of constants using an enumerated list enum {Mon, Tue, Wed, Thr, Fri, Sat