Migration: migration from Caps to OP

Author: Saisang

TOC.md

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+---
+title: "#define Directive (C-C++)"
+ms.custom: na
+ms.date: 10/03/2016
+ms.devlang: 
+  - C++
+  - C
+ms.prod: visual-studio-dev14
+ms.reviewer: na
+ms.suite: na
+ms.technology: 
+  - devlang-cpp
+ms.tgt_pltfrm: na
+ms.topic: article
+H1: #define Directive (C/C++)
+ms.assetid: 33cf25c6-b24e-40bf-ab30-9008f0391710
+caps.latest.revision: 13
+manager: ghogen
+translation.priority.ht: 
+  - cs-cz
+  - de-de
+  - es-es
+  - fr-fr
+  - it-it
+  - ja-jp
+  - ko-kr
+  - pl-pl
+  - pt-br
+  - ru-ru
+  - tr-tr
+  - zh-cn
+  - zh-tw
+---
+# #define Directive (C-C++)
+The `#define` creates a *macro*, which is the association of an identifier or parameterized identifier with a token string. After the macro is defined, the compiler can substitute the token string for each occurrence of the identifier in the source file.  
+  
+## Syntax  
+ `#define` *identifier* *token-string*opt  
+  
+ `#define` *identifier* `(` *identifier*opt`,`*...*`,`*identifier*opt`)`*token-string*opt  
+  
+## Remarks  
+ The `#define` directive causes the compiler to substitute *token-string* for each occurrence of *identifier* in the source file. The *identifier* is replaced only when it forms a token. That is, *identifier* is not replaced if it appears in a comment, in a string, or as part of a longer identifier. For more information, see [Tokens](../VS_visualcpp/Tokens--C---.md).  
+  
+ The *token-string* argument consists of a series of tokens, such as keywords, constants, or complete statements. One or more white-space characters must separate *token-string* from *identifier*. This white space is not considered part of the substituted text, nor is any white space that follows the last token of the text.  
+  
+ A `#define` without a *token-string* removes occurrences of *identifier* from the source file. The *identifier* remains defined and can be tested by using the `#if defined` and `#ifdef` directives.  
+  
+ The second syntax form defines a function-like macro with parameters. This form accepts an optional list of parameters that must appear in parentheses. After the macro is defined, each subsequent occurrence of *identifier*( *identifier*opt, ..., *identifier*opt ) is replaced with a version of the *token-string* argument that has actual arguments substituted for formal parameters.  
+  
+ Formal parameter names appear in *token-string* to mark the locations where actual values are substituted. Each parameter name can appear multiple times in *token-string*, and the names can appear in any order. The number of arguments in the call must match the number of parameters in the macro definition. Liberal use of parentheses guarantees that complex actual arguments are interpreted correctly.  
+  
+ The formal parameters in the list are separated by commas. Each name in the list must be unique, and the list must be enclosed in parentheses. No spaces can separate *identifier* and the opening parenthesis. Use line concatenation — place a backslash (`\`) immediately before the newline character — for long directives on multiple source lines. The scope of a formal parameter name extends to the new line that ends *token-string*.  
+  
+ When a macro has been defined in the second syntax form, subsequent textual instances followed by an argument list indicate a macro call. The actual arguments that follows an instance of *identifier* in the source file are matched to the corresponding formal parameters in the macro definition. Each formal parameter in *token-string* that is not preceded by a stringizing (`#`), charizing (`#@`), or token-pasting (`##`) operator, or not followed by a `##` operator, is replaced by the corresponding actual argument. Any macros in the actual argument are expanded before the directive replaces the formal parameter. (The operators are described in [Preprocessor Operators](../VS_visualcpp/Preprocessor-Operators.md).)  
+  
+ The following examples of macros with arguments illustrate the second form of the `#define` syntax:  
+  
+```  
+// Macro to define cursor lines   
+#define CURSOR(top, bottom) (((top) << 8) | (bottom))  
+  
+// Macro to get a random integer with a specified range   
+#define getrandom(min, max) \  
+    ((rand()%(int)(((max) + 1)-(min)))+ (min))  
+```  
+  
+ Arguments with side effects sometimes cause macros to produce unexpected results. A given formal parameter may appear more than one time in *token-string*. If that formal parameter is replaced by an expression with side effects, the expression, with its side effects, may be evaluated more than one time. (See the examples under [Token-Pasting Operator (##)](../VS_visualcpp/Token-Pasting-Operator--##-.md).)  
+  
+ The `#undef` directive causes an identifier's preprocessor definition to be forgotten. See [The #undef Directive](../VS_visualcpp/#undef-Directive--C-C---.md) for more information.  
+  
+ If the name of the macro being defined occurs in *token-string* (even as a result of another macro expansion), it is not expanded.  
+  
+ A second `#define` for a macro with the same name generates a warning unless the second token sequence is identical to the first.  
+  
+ **Microsoft Specific**  
+  
+ Microsoft C/C++ lets you redefine a macro if the new definition is syntactically identical to the original definition. In other words, the two definitions can have different parameter names. This behavior differs from ANSI C, which requires that the two definitions be lexically identical.  
+  
+ For example, the following two macros are identical except for the parameter names. ANSI C does not allow such a redefinition, but Microsoft C/C++ compiles it without error.  
+  
+```  
+#define multiply( f1, f2 ) ( f1 * f2 )  
+#define multiply( a1, a2 ) ( a1 * a2 )  
+```  
+  
+ On the other hand, the following two macros are not identical and will generate a warning in Microsoft C/C++.  
+  
+```  
+#define multiply( f1, f2 ) ( f1 * f2 )  
+#define multiply( a1, a2 ) ( b1 * b2 )  
+```  
+  
+ **END Microsoft Specific**  
+  
+ This example illustrates the `#define` directive:  
+  
+```  
+#define WIDTH       80  
+#define LENGTH      ( WIDTH + 10 )  
+```  
+  
+ The first statement defines the identifier `WIDTH` as the integer constant 80 and defines `LENGTH` in terms of `WIDTH` and the integer constant 10. Each occurrence of `LENGTH` is replaced by (`WIDTH + 10`). In turn, each occurrence of `WIDTH + 10` is replaced by the expression (`80 + 10`). The parentheses around `WIDTH + 10` are important because they control the interpretation in statements such as the following:  
+  
+```  
+var = LENGTH * 20;  
+```  
+  
+ After the preprocessing stage the statement becomes:  
+  
+```  
+var = ( 80 + 10 ) * 20;  
+```  
+  
+ which evaluates to 1800. Without parentheses, the result is:  
+  
+```  
+var = 80 + 10 * 20;  
+```  
+  
+ which evaluates to 280.  
+  
+ **Microsoft Specific**  
+  
+ Defining macros and constants with the [/D](../VS_visualcpp/-D--Preprocessor-Definitions-.md) compiler option has the same effect as using a `#define` preprocessing directive at the start of your file. Up to 30 macros can be defined by using the /D option.  
+  
+ **END Microsoft Specific**  
+  
+## See Also  
+ [Preprocessor Directives](../VS_visualcpp/Preprocessor-Directives.md)

VS_visualcpp/#define-Directive--C-C---.md

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+---
+title: "#error Directive (C-C++)"
+ms.custom: na
+ms.date: 10/03/2016
+ms.devlang: 
+  - C++
+  - C
+ms.prod: visual-studio-dev14
+ms.reviewer: na
+ms.suite: na
+ms.technology: 
+  - devlang-cpp
+ms.tgt_pltfrm: na
+ms.topic: article
+H1: #error Directive (C/C++)
+ms.assetid: d550a802-ff19-4347-9597-688935d23b2b
+caps.latest.revision: 8
+manager: ghogen
+translation.priority.ht: 
+  - cs-cz
+  - de-de
+  - es-es
+  - fr-fr
+  - it-it
+  - ja-jp
+  - ko-kr
+  - pl-pl
+  - pt-br
+  - ru-ru
+  - tr-tr
+  - zh-cn
+  - zh-tw
+---
+# #error Directive (C-C++)
+The `#error` directive emits a user-specified error message at compile time and then terminates the compilation.  
+  
+## Syntax  
+  
+```  
+#errortoken-string  
+```  
+  
+## Remarks  
+ The error message that this directive emits includes the *token-string* parameter. The `token-string` parameter is not subject to macro expansion. This directive is most useful during preprocessing for notifying the developer of a program inconsistency or the violation of a constraint. The following example demonstrates error processing during preprocessing:  
+  
+```  
+#if !defined(__cplusplus)  
+#error C++ compiler required.  
+#endif  
+```  
+  
+## See Also  
+ [Preprocessor Directives](../VS_visualcpp/Preprocessor-Directives.md)

VS_visualcpp/#error-Directive--C-C---.md

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+---
+title: "#if, #elif, #else, and #endif Directives (C-C++)"
+ms.custom: na
+ms.date: 10/03/2016
+ms.devlang: 
+  - C++
+  - C
+ms.prod: visual-studio-dev14
+ms.reviewer: na
+ms.suite: na
+ms.technology: 
+  - devlang-cpp
+ms.tgt_pltfrm: na
+ms.topic: article
+H1: #if, #elif, #else, and #endif Directives (C/C++)
+ms.assetid: c77a175f-6ca8-47d4-8df9-7bac5943d01b
+caps.latest.revision: 10
+manager: ghogen
+translation.priority.ht: 
+  - cs-cz
+  - de-de
+  - es-es
+  - fr-fr
+  - it-it
+  - ja-jp
+  - ko-kr
+  - pl-pl
+  - pt-br
+  - ru-ru
+  - tr-tr
+  - zh-cn
+  - zh-tw
+---
+# #if, #elif, #else, and #endif Directives (C-C++)
+The `#if` directive, with the `#elif`, `#else`, and `#endif` directives, controls compilation of portions of a source file. If the expression you write (after the `#if`) has a nonzero value, the line group immediately following the `#if` directive is retained in the translation unit.  
+  
+## Grammar  
+ *conditional* :  
+ *if-part elif-parts*opt*else-part*opt*endif-line*  
+  
+ *if-part* :  
+ *if-line text*  
+  
+ *if-line* :  
+ **#if**  *constant-expression*  
+  
+ **#ifdef**  *identifier*  
+  
+ **#ifndef**  *identifier*  
+  
+ *elif-parts* :  
+ *elif-line text*  
+  
+ *elif-parts elif-line text*  
+  
+ *elif-line* :  
+ **#elif**  *constant-expression*  
+  
+ *else-part* :  
+ *else-line text*  
+  
+ *else-line* :  
+ `#else`  
+  
+ *endif-line* :  
+ `#endif`  
+  
+ Each `#if` directive in a source file must be matched by a closing `#endif` directive. Any number of `#elif` directives can appear between the `#if` and `#endif` directives, but at most one `#else` directive is allowed. The `#else` directive, if present, must be the last directive before `#endif`.  
+  
+ The `#if`, `#elif`, `#else`, and `#endif` directives can nest in the text portions of other `#if` directives. Each nested `#else`, `#elif`, or `#endif` directive belongs to the closest preceding `#if` directive.  
+  
+ All conditional-compilation directives, such as `#if` and **#ifdef**, must be matched with closing `#endif` directives prior to the end of file; otherwise, an error message is generated. When conditional-compilation directives are contained in include files, they must satisfy the same conditions: There must be no unmatched conditional-compilation directives at the end of the include file.  
+  
+ Macro replacement is performed within the part of the command line that follows an `#elif` command, so a macro call can be used in the *constant-expression*.  
+  
+ The preprocessor selects one of the given occurrences of *text* for further processing. A block specified in *text* can be any sequence of text. It can occupy more than one line. Usually *text* is program text that has meaning to the compiler or the preprocessor.  
+  
+ The preprocessor processes the selected *text* and passes it to the compiler. If *text* contains preprocessor directives, the preprocessor carries out those directives. Only text blocks selected by the preprocessor are compiled.  
+  
+ The preprocessor selects a single *text* item by evaluating the constant expression following each `#if` or `#elif` directive until it finds a true (nonzero) constant expression. It selects all text (including other preprocessor directives beginning with **#**) up to its associated `#elif`, `#else`, or `#endif`.  
+  
+ If all occurrences of *constant-expression* are false, or if no `#elif` directives appear, the preprocessor selects the text block after the `#else` clause. If the `#else` clause is omitted and all instances of *constant-expression* in the `#if` block are false, no text block is selected.  
+  
+ The *constant-expression* is an integer constant expression with these additional restrictions:  
+  
+-   Expressions must have integral type and can include only integer constants, character constants, and the **defined** operator.  
+  
+-   The expression cannot use `sizeof` or a type-cast operator.  
+  
+-   The target environment may not be able to represent all ranges of integers.  
+  
+-   The translation represents type `int` the same as type **long**, and `unsigned int` the same as `unsigned long`.  
+  
+-   The translator can translate character constants to a set of code values different from the set for the target environment. To determine the properties of the target environment, check values of macros from LIMITS.H in an application built for the target environment.  
+  
+-   The expression must not perform any environmental inquiries and must remain insulated from implementation details on the target computer.  
+  
+ The preprocessor operator **defined** can be used in special constant expressions, as shown by the following syntax:  
+  
+ defined( `identifier` )  
+  
+ defined `identifier`  
+  
+ This constant expression is considered true (nonzero) if the *identifier* is currently defined; otherwise, the condition is false (0). An identifier defined as empty text is considered defined. The **defined** directive can be used in an `#if` and an `#elif` directive, but nowhere else.  
+  
+ In the following example, the `#if` and `#endif` directives control compilation of one of three function calls:  
+  
+```  
+#if defined(CREDIT)  
+    credit();  
+#elif defined(DEBIT)  
+    debit();  
+#else  
+    printerror();  
+#endif  
+```  
+  
+ The function call to `credit` is compiled if the identifier `CREDIT` is defined. If the identifier `DEBIT` is defined, the function call to `debit` is compiled. If neither identifier is defined, the call to `printerror` is compiled. Note that `CREDIT` and `credit` are distinct identifiers in C and C++ because their cases are different.  
+  
+ The conditional compilation statements in the following example assume a previously defined symbolic constant named `DLEVEL`.  
+  
+```  
+#if DLEVEL > 5  
+    #define SIGNAL  1  
+    #if STACKUSE == 1  
+        #define STACK   200  
+    #else  
+        #define STACK   100  
+    #endif  
+#else  
+    #define SIGNAL  0  
+    #if STACKUSE == 1  
+        #define STACK   100  
+    #else  
+        #define STACK   50  
+    #endif  
+#endif  
+#if DLEVEL == 0  
+    #define STACK 0  
+#elif DLEVEL == 1  
+    #define STACK 100  
+#elif DLEVEL > 5  
+    display( debugptr );  
+#else  
+    #define STACK 200  
+#endif  
+```  
+  
+ The first `#if` block shows two sets of nested `#if`, `#else`, and `#endif` directives. The first set of directives is processed only if `DLEVEL > 5` is true. Otherwise, the statements after #**else** are processed.  
+  
+ The `#elif` and `#else` directives in the second example are used to make one of four choices, based on the value of `DLEVEL`. The constant `STACK` is set to 0, 100, or 200, depending on the definition of `DLEVEL`. If `DLEVEL` is greater than 5, then the statement  
+  
+```  
+#elif DLEVEL > 5  
+display(debugptr);  
+```  
+  
+ is compiled and `STACK` is not defined.  
+  
+ A common use for conditional compilation is to prevent multiple inclusions of the same header file. In C++, where classes are often defined in header files, constructs like the following can be used to prevent multiple definitions:  
+  
+```  
+/*  EXAMPLE.H - Example header file  */  
+#if !defined( EXAMPLE_H )  
+#define EXAMPLE_H  
+  
+class Example  
+{  
+...  
+};  
+  
+#endif // !defined( EXAMPLE_H )  
+```  
+  
+ The preceding code checks to see if the symbolic constant `EXAMPLE_H` is defined. If so, the file has already been included and need not be reprocessed. If not, the constant `EXAMPLE_H` is defined to mark EXAMPLE.H as already processed.  
+  
+## See Also  
+ [Preprocessor Directives](../VS_visualcpp/Preprocessor-Directives.md)