Preprocessor directives. Preprocessor directives are lines included in the code of programs preceded by a hash sign (#).
These lines are not program statements but directives for the preprocessor. The preprocessor examines the code before actual compilation of code begins and resolves all these directives before any code is actually generated by regular statements. These preprocessor directives extend only across a single line of code. As soon as a newline character is found, the preprocessor directive is ends. No semicolon (;) is expected at the end of a preprocessor directive. Macro definitions (#define, #undef) To define preprocessor macros we can use #define. #define identifier replacement When the preprocessor encounters this directive, it replaces any occurrence of identifier in the rest of the code by replacement. After the preprocessor has replaced TABLE_SIZE, the code becomes equivalent to: #define can work also with parameters to define function macros: This would generate the same code as: For example:
Using C and C++ preprocessor directives more program examples on. |< C & C++ Preprocessor Directives 1 | Main | C & C++ Type Specifiers >| Site Index | Download | THE C/C++ PREPROCESSOR DIRECTIVES 2: #define etc.
The C/C++ preprocessor directives programming skills that should be acquired: Then correct the error by defining MyVal to 2 as the following program and when you rebuild, it should be OK. // the #error directive... #include <stdio.h> #IF ... #ENDIF Preprocessor Directive. Conditionally includes source code at compile-time.
#IF nExpression1 | lExpression1 Commands [#ELIF nExpression2 | #ELIF lExpression2 Commands... #ELIF nExpressionN | #ELIF lExpressionN Commands] [#ELSE Commands] #ENDIF Parameters #IF nExpression1| lExpression1Commands nExpression1 specifies the numeric expression that is evaluated. If the expression is nonzero, the commands immediately following #IF are included in the compiled code. lExpression1 specifies the logical expression that is evaluated. Comment utiliser le message # pragma pour générer des messages d'avertissement défini par l'utilisateur dans Visual C++
In some instances, you may find it advantageous to have the compiler generate user-defined warning messages such as the following: collisions.cpp(1) : Warning Msg: Need to do 3-D collision checking When such a warning is generated by the compiler and displayed in the Developer Studio's Output window, you can double-click on the warning message to get to the line of code with the message.
Preprocessor and sizeof() - C / C++ answers. In article <1159544737.391377.26810@h48g2000cwc.googlegroups. com>, Amigo >I started working on an embedded project a few ago on Freescale 16-bitmicro with an IAR toolset.
Running PolySpace for the project codehighlighted amongst other things a peculiar construct in one of thecompiler's header files. Here's the code snippet:#ifndef __SIZE_T_TYPE__#if sizeof((char*)0 - (char*)0) <= sizeof(int) [snippage; this is a somewhat bizarre way of "re-guessing" the compiler's internal type for size_t] >I was very suspicious about this construct in the first place ...
It is good to be suspicious of this. The C standard tells us that, during the preprocessing phases, keywords do not exist. #if burble((gank*)0 - (gank*)0) <= burble(mud) Each identifier is then replaced with the integer value 0, giving: Allocation de mémoire sécurisée en C et Cpp - Haypo. #pragma message("my merssage") Sends a string literal to the standard output without terminating the compilation.
#pragma message( messagestring ) A typical use of the message pragma is to display informational messages at compile time. The messagestring parameter can be a macro that expands to a string literal, and you can concatenate such macros with string literals in any combination. If you use a predefined macro in the message pragma, the macro should return a string, else you will have to convert the output of the macro to a string. Vous pouvez utiliser # pragma comment(lib...) pour spécifier des options de l'éditeur de liens dans Microsoft C++ Le pragma commentaire permet à l'utilisateur d'insérer des commentaires dans un fichier exécutable ou un fichier de l'objet.
Le spécificateur de lib permet à l'utilisateur de passer ce commentaire à l'éditeur de liens pour spécifier des bibliothèques supplémentaires à lier lorsque vous utilisez le module objet. Certains utilisateurs utilisent le pragma commentaire lib pour ajouter des options de l'éditeur de liens ainsi que les noms de bibliothèques, telles que : #pragma comment(lib, "MSVCRT -VERBOSE") Cette ligne, sous Visual C++ 2.x, transmettez la chaîne à l'éditeur de liens comme, ce qui entraîne l'ajout de la /VERBOSE option éditeur de liens, ainsi que le MSVCRT.Bibliothèque de LIB. Ce comportement n'a pas été spécifié pour travailler de cette manière. Dans Visual C++ 4.x et version ultérieure, le compilateur place correctement des guillemets autour de la chaîne de commentaire provoquant ainsi le code ci-dessus pour générer l'erreur suivante : Traduction automatique.