Example: #include <iostream> #include "project.h" #if VERSION == 1 #define MYPROJ_H "version1.h" #else #define MYPROJ_H "version2.h" #endif #include MYPROJ_H The #if, #elif, #else, and #endif Directives You can use the #if, #elif, and #endif directives to compile certain parts of a source file and ignore others. The directives are known as conditional compilation directives for this reason. Syntax: #if expression1 [text1] [#elif expression2 text2] . . [#elif expression(n) text(n)] [#else text(n+1)] #endif Each #if directive must be terminated by an #endif directive. Multiple #elif direc- tives can occur in between. The #else directive can occur once only. The preprocessor evaluates expression1, expression2, in sequence. If an expression that yields “true” is found, that is its value is not 0, the corresponding code for this expression is processed. If none of these expressions is true, the #else directive is executed. If this directive is omitted, no corresponding code is processed. expression1, expression1, must be constant expressions of integral types and cannot contain the cast operator. Some compilers do not allow the use of the sizeof operator. The corresponding text is a source text, that is, it comprises preprocessor directives, C++ statements, or whole C++ programs. When a corresponding text is processed, the preprocessor may first execute directives before passing the expanded source code to the compiler for compilation. Code that the preprocessor has not processed is removed from the source. PREPROCESSOR DIRECTIVES ■ 789 The defined Operator You can use the defined operator to check whether a symbolic constant or macro has been defined. Syntax: defined(name) The operator returns a value other than 0 if valid definition for name exists, and the value 0 in all other cases. A definition created using the #define directive remains valid until it is removed by an #undef directive. If the substitute text following name in the #define directive is missing, the definition is still valid. The defined operator is normally used in #if or #elif directives, for example Example: #if defined VERSION Using the defined operator allows you to use its return value in a preprocessor expres- sion. The #ifdef and #ifndef Directives You can also perform the same check using the #ifdef and #ifndef directives. Syntax: #ifdef name #ifndef name The #ifdef directive returns a value other than 0 if name is defined and otherwise 0. In contrast, the #ifndef directive ensures that a value has not yet been defined, that is, that name is undefined, returning 0 if name has been defined, and a non-zero value in any other case. Example: #if defined(STATE) && defined(COND) . . . The #line Directive The compiler uses line numbers and the name of a source file to display errors discovered on compilation. You can use the #line directive to change the line numbers and the file name. Syntax: #line new_number ["filename"] At this position a new line count begins by new_number. If filename is stated, it will become the new file name that the compiler refers to when issuing error messages. The new file name must be in quotes and new_number must be an integral constant. Example: #line 170 "genprog1.cpp" The line number and the file name can also be stated as symbolic constants. 790 ■ APPENDIX Example: #if VERSION == 1 #define NEWNUMBER 20 #else #define NEWNUMBER 25 #line NEWNUMBER The #line directive is often used by program generators compiling code to produce a C++ program. In the case of error messages, the message can refer to the appropriate line and file name in the original code. The current line number and file name can be accessed using the standard macros __LINE__ and __FILE__. Example: cout << "Current line number: " << __LINE__ << endl << "File name: " << __FILE__ << endl; The #error Directive The #error directive can be used to show preprocessor errors. Syntax: #error errortext; The message errortext is issued and compilation is terminated. Example: #if defined VERSION #if VERSION < 3 #error VERSION too old.\n ##error Version 3 or better needed. #endif #include "version.h" If the symbolic constant VERSION is defined and the value is less than 3, the following error message is output: VERSION too old. Version 3 or better needed. The #pragma Directive The #pragma directive is compiler dependent and allows you to define your own pre- processor commands for a specific compiler. Syntax: #pragma command Any other compiler that supports the #pragma directive but does not support the com- mand following #pragma simply ignores the command. Example: #pragma pack(1) This directive causes a Microsoft compiler to align the components of a class bytewise, avoiding gaps. Other options are pack(2) and pack(4). PREPROCESSOR DIRECTIVES ■ 791 ■ PRE-DEFINED STANDARD MACROS The ANSI standard provides for six pre-defined standard macros. Their names begin and end with two underscores: __LINE__ Returns the number of the line containing the __LINE__ macro. The first line in a source code is line 1. The numbering can be modified using the #line directive. __FILE__ Returns the name of the source file that contains the __FILE__ macro. The name can be modified using the #line directive. __DATE__ Returns the date in the mmm dd yyyy format, where mmm is an abbreviation for the month, dd is the day of the month, and yyyy is the year, resulting in Jul 17 2001, for example. __DATE__ refers to the point in time when the preprocessor started processing the source. Thus, the macro returns the same result at any position in the source code. __TIME__ Returns the time as a string in the format hh:mm:ss, where hh refers to hours, mm to minutes, and ss to seconds, e.g., 15:23:47. __TIME__ refers to the point in time when the preprocessor started processing the source. Thus, the macro returns the same result at any position in the source code. __STDC__ Is only defined if the source code contains ANSI keywords only. __cplusplus Is defined if the source code is compiled using a C++ compiler. 792 ■ APPENDIX ■ BINDING C FUNCTIONS Calling C Functions in C++ Programs C functions from C libraries can be called in a C++ program. However, function calls are interpreted differently by the C++ compiler than you would expect from a C compiler. You must therefore supply additional binding information that is accessible via an extern "C" declaration. Example: extern "C" void oldfunc(int size); This informs the C++ compiler that a C compiler was used to compile the oldfunc() function. If you need to declare multiple C functions, you can declare their prototypes after extern "C" within curved brackets. If you have already declared the functions in a header file, you can include the header file in an extern "C" block. Example: extern "C" { #include "graphic.h" } It is common practise to declare extern "C" code in C header files. You can then include the C header both in C and in C++ programs. Example: #if defined _cplusplus extern "C" { #endif // Prototypes for C functions here #if defined __cplusplus } #endif The symbolic constant __cplusplus is evaluated to discover whether the current compiler is a C or C++ compiler. If __cplusplus is defined, that is, a C++ compiler is active, the extern "C" block is inserted. Defining C Functions in C++ Programs It is also possible to define your own C functions for a C++ program. You need to do this if you call a function that expects a C function as an argument, such as the standard qsort() and bsearch() functions. The definition for a C function in a C++ program must be encased in an extern "C" block. This instructs the compiler to compile the function as a C function. BINDING C FUNCTIONS ■ 793 Example: #include <string> #include <iostream> #include <cstdlib> using namespace std; static char* city[] = { "Paris", "London", "Barcelona", "Hollywood"} static char* key = "New York"; extern "C" int scmp(const void*, const void*); int main() { // Sort cities: qsort( city, 4, sizeof(char*), scmp); // Find city: if( bsearch( &key, city, 4, sizeof(char*),scmp) == NULL) cout << "City" << (string) key << "not found.\n"; } extern "C" { int scmp(const void *s1, const void *s2) { return strcmp( *(const char**)s1, *(const char**)s2 ); } } The C function scmp() is passed to the standard functions bsearch() for binary searching and qsort() for sorting using the quick sort algorithm. 794 ■ APPENDIX ■ OPERATORS OVERVIEW Operator Meaning Arithmetical Operators: Relational Operators: Logical Operators: Assignment Operators: Bit-wise operators: addition, subtraction multiplication division, modulus division unary plus, minus operator increment, decrement operator + * / + ++ - % - “equal”, “unequal” “less”, “less or equal” “greater”, “greater or equal” == < > != <= >= AND, OR NOT && ! || AND, NOT OR, exclusive-OR left shift, right shift & | << ~ ^ >> simple assignment compound assignment (op is a binary arithmetical or binary bit-wise operator) = op= OPERATORS OVERVIEW ■ 795 ■ OPERATORS OVERVIEW (CONTINUED) Operator Meaning Access Operators: Cast Operators: Operators for Storage Allocation Other Operators: scope resolution operator subscript operator indirection operator class member access operators pointer to member operators :: [] * . .* -> ->* C cast operator dynamic cast operator static cast operator const cast operator reinterpret cast operator conditional expression and comma operator address-of operator call to function name create a temporary object of type type sizeof operator (size of type) typeid operator (type informations) To allocate storage dynamically for an object, an array resp. To free dynamically allocated storage for an object, an array resp. (type) dynamic_cast<> static_cast<> const_cast<> reinterpret_cast<> new delete new [] delete [] ?: & name() type() sizeof() typeid() , 796 ■ APPENDIX ■ OPERATOR PRECEDENCE TABLE OperatorPrecedence Grouping 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16. 17. from left to right from left to right from left to right from left to right from left to right from left to right from left to right from left to right from left to right from left to right from left to right from left to right from left to right from left to right from right to left from right to left from right to left :: ! .* * >> < == ^ | || != <= > >= << /% ->* ~ >[] ++("postfix") + ("unary") + ("binary") - ("binary") & ("bit-wise AND") && ?: = %= += -= *= /= &= , ^= |= <<= >>= - ( "unary") ++ ("prefix") - ( "prefix") & ("address") * ( "indirection") – –("postfix") name() typeid() type() dynamic_cast<> static_cast<> const_cast<> reinterpret_cast<> new new[] delete delete[] (type) sizeof() OPERATOR PRECEDENCE TABLE ■ 797 ■ ASCII CODE TABLE decimal octal hex character decimal octal hex character 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 20 21 22 23 24 25 26 27 28 29 2A 2B 2C 2D 2E 2F 30 31 32 33 34 35 36 37 38 39 3A 3B 3C 3D 3E 3F (BLANK) ! " # $ % & ' ( ) * + , - . / 0 1 2 3 4 5 6 7 8 9 : ; < = > ? 040 041 042 043 044 045 046 047 050 051 052 053 054 055 056 057 060 061 062 063 064 065 066 067 070 071 072 073 074 075 076 077 000 001 002 003 004 005 006 007 010 011 012 013 014 015 016 017 020 021 022 023 024 025 026 027 030 031 032 033 034 035 036 037 00 01 02 03 04 05 06 07 08 09 A B C D E F 10 11 12 13 14 15 16 17 18 19 1A 1B 1C 1D 1E 1F (NUL) (SOH) (STX) (ETX) (EOT) (ENQ) (ACK) (BEL) (BS) (HT) (LF) (VT) (FF) (CR) (SO) (SI) (DLE) (DC1) (DC2) (DC3) (DC4) (DC5) (SYN) (ETB) (CAN) (EM) (SUB) (ESC) (FS) (GS) (RS) (US) 798 ■ APPENDIX . operator dynamic cast operator static cast operator const cast operator reinterpret cast operator conditional expression and comma operator address-of operator call to function name create a temporary. assignment compound assignment (op is a binary arithmetical or binary bit-wise operator) = op= OPERATORS OVERVIEW ■ 795 ■ OPERATORS OVERVIEW (CONTINUED) Operator Meaning Access Operators: Cast Operators: Operators. temporary object of type type sizeof operator (size of type) typeid operator (type informations) To allocate storage dynamically for an object, an array resp. To free dynamically allocated storage for