define defragment

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

C Language # define keywords, Conditional compilation and predefined symbolic knowledge details,I. pre-defined symbols The C standard defines the following five preprocessing symbols _ FILE _ // name of the source FILE to be compiled _ LINE _/current row number of the FILE _ DATE _/DATE of FILE compilation _ TIME __/ /file Compilation Time _ STDC _ // If the compiler complies with ansi c, the value is 1. Otherwise, it is undefined. We will use these p

When we look at some open-source code, we often see the following scenarios:# If defined (_ PTHREADS )! Defined (_ NOTHREADS)# Define _ STL_PTHREADS# Endif# If defined (_ UITHREADS )! Defined (_ PTHREADS )! Defined (_ NOTHREADS)# Define _ STL_UITHREADS# Endif# If defined (_ sgi )! Defined (_ GNUC __)# Include # If! Defined (_ BOOL)# Define _ STL_NO_BOOL# Endif# I

Const and define constants in php, but what are their specific differences? In fact, it is very simple to use const for class member variable definition. once defined and its value cannot be changed, define defines global constants and can access page d anywhere... const and define constants in php, but what are their specific differences? In fact, it is very sim

the difference between #define和inlineDefine: defines a macro that is processed during precompilation ;Simple character substitution, no type detectiontypedef: defining type aliases for handling complex typesExample: typedef int A;Then: a A;//define A as intInline: Inline functions advise the compiler whether to replace macros, and the compiler has the right to denyIt is not necessarily successful to make an

You may not know, define, declare, initialize, declare Initialization Declaration definitions are everywhere, but they are not as simple as they are.First, from a broad perspective, a declaration contains a definition, which can also be referred to as a "declarative definition". In a narrow sense, a declaration can be called a "reference Declaration ".Next, we will discuss "declarative definition" and "reference Declaration ". Definition and declarati

XML SchemaUsage 1. Define the elements in an XML document 2. Define the attributes in an XML document. 3. Define what kind of sub-nodes are available for a node, how many sub-nodes are available, and the sequence in which the sub-nodes appear 4. Define the Data Type of the element or attribute 5.

Define: Define macros processed during pre-Compilation; Only simple character replacement, no type detection Typedef:Define the type alias for processing complex typesExample: typedef int;Then: A; // defines a as Int. Inline:The inline function provides suggestions to the compiler. the compiler has the right to reject the macro replacement. Not necessarily succeeded in submitting an application StaticI.

Usage and differentiation of typedef and # defineI. Usage of typedefA typedef is commonly used to define an identifier and an alias for a keyword in the C + + language, which is part of the language compilation process, but it does not actually allocate memory space, such as:typedef int INT;typedef int ARRAY[10];typedef (INT*) PINT;typedef can enhance the readability of the program, as well as the flexibility of identifiers, but it also has a "non-int

In this paper, we mainly record the pre-C + + preprocessor directives, and the common preprocessing directives are: #空指令, without any effect #include包含一个源代码文件 #define定义宏 #undef取消已定义的宏 #if如果给定条件为真, the following code is compiled #ifdef如果宏已经定义, the following code is compiled #ifndef如果宏没有定义, the following code is compiled #elif如果前面的 # If the given condition is not true and the current condition is true, compile the fo

The so-called constant is a simple identifier. The value cannot be changed during script execution. Constants are case sensitive by default. Usually, constant identifiers are always uppercase. Constants can only contain scalar data (Boolean, Integer, float, and string). You can define resource constants, but avoid them as much as possible, because they cause unpredictable results. Define partMacros can be