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The difference between define () and const: Define () defines constants during the execution period, while Const defines constants at compile time. This will have a slight speed advantage (ie a slightly better performance), but it is not worth considering unless you are building a large, high concurrency system. Define () puts constants into the global scope, e

# Define is a macro definition Command provided in C language. Its main purpose is to provide programmers with some convenience in programming and improve the program running efficiency to a certain extent, however, students often cannotUnderstanding the essence of this command always creates some confusion here. This command is misused during programming to make the program run differently from the expected purpose, or when reading a program written

. Let's take a closer look at the msdn example and have a good understanding. The following is an example of how to define a Unified Version macro. Assume that the project contains the resource script file resource. RC, and the unique version number is stored in define. h. Other CPP files that require version numbers contain this file. Let's take a look at define

From: Http://stackoverflow.com/questions/2447791/define-vs-constSame point: Both can define constantsConst foo = ' Bar ';d efind (' foo ', ' Bar ');The disadvantage of const:1.const must be declared in Top-level-scope (top-level domain):For example:if (condition) { const FOO = ' BAR '; // Not defined }// but if(condition) { defind (/// definition }A common detection constant is d

Parse the differences between const and define in php. 1. const is used for defining class member variables. once defined, the value cannot be changed. Define defines global constants that can be accessed anywhere. 2. define cannot be defined in the class, but const can. 1. const is used for defining class member variables. once defined, the value cannot be chang

TypedefIt is a type-defined keyword that is used to declare Custom Data Types in computer programming languages and used with various original data types to simplify programming. #DefineIs a preprocessing command. Let's take a look. Typedef is a C language statement that allows you to take an "alias" for an existing data type ". For example: typedefintINTEGER； After that, INTEGER can be used to replace int as the type of the INTEGER variable, for example: INTEGERa,b; Using typede

C #-# define condition compilation, Introduction: C # pre-processor commands will never be converted into executable code commands, but will affect all aspects of the compilation process. Commonly used pre-processor Commands include # define, # undef, # if, # elif, # else and # endif, etc. The following describes the example of using # define in C # For Condition

1 similarities and differences as constants (0) SameBoth can be used to define constants;#define PI 3.14159//Macro ConstantsConst DOULBE pi=3.14159; Constant(1) different compiler processing methodsThe Define macro is expanded in the preprocessing stage;Const constants are used in the compile run phase;(2) Different types and security checksDefine macros have no

Let's say the following code is required to be compatible with three versionsThis will not complete the task.No mattertypedef enum{first,second,third,}; #define NUM third#if (num = = first) #define VAR 1#elif (num = = SECOND) # Define var 2#elif (num = = third) #define var 3#endifint main (void) {#if (num = = fi

What do we often do with define? 1) define a constant 2) define a macro Why do not use define. The following two aspects are explained: 1) when we define a constant, we can use the following method: # Define aspect_patio

Q: How do I define global variables in VC? A:Put in any fileUse extern declaration in other filesOr declare a Public Member in the App class.It can be used in other classes of the program.AfxGetApp () gets an App object pointer and converts it to your App class pointer.Then you can use the pointer-> variableIn additionThe class defined in MFC only for static members can be directly applied at that time.Damaged Structure A: You can also create a. h hea

Try to use const and inline instead of # define This clause is best referred to as "try to use the compiler instead of preprocessing", because # define is often considered not part of the language itself. This is one of the problems. Let's look at the following statement: # Define aspect_ratio 1.653 The compiler will never see the aspect_ratio symbol name, becaus

Http://blog.csdn.net/zhanglianpin Global variables should be variables that are allocated in memory and can be called by other modules using the extern keyword in C language. Therefore, it must be defined in the. C and. H files. This repetitive definition can easily lead to errors. The following methods can be defined only once in the header file. Although it is a bit difficult to understand, once the user Master, it is flexible to use. The definitions in Table 1.2 appear in the. h header file t

For a long time, macro definition # define is used to define some simple constants. At most, it is used to define a function. It seldom pays attention to macro definition usage. Until the following code is displayed: #define PLAYSOUNDEFFECT(...) \[[GameManager sharedGameManager] playSoundEffect:@#__VA_ARGS__] I have

The difference between define () and const in php is described in detail. In php, both define () and const () can define constants. So what is the difference between define () and const? many programmers do not understand this, next I will introduce some differences between define