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In iOS development, it is often used to define macros, or to modify some data types with const, and often developers do not know how to use them correctly, resulting in the confusion of macros and const decorations in the project.Can you tell the difference between the following? Do you know when to use it?#define Hscoder @ "Hansha haha"NSString*hscoder = @"Hansha haha";extern NSString*hscoder;extern Const

typedefIf it is placed outside all functions, its scope is from the beginning of its definition until the end of the file;If placed within a function, the defined field is defined from the beginning of the definition until the end of the function;#define:Scopes are defined from the beginning of the definition to the end of the entire file, whether within a function or outside of all functions.Define within the same compilation unit, even in different namespaces, the scope of the action is the sa

The difference is as follows: Constants defined with #define MAX 255 are of no type , given an immediate number, and the compiler simply links the defined constant value to the name of the defined constant, define the defined macro variable to be replaced at the time of preprocessing. Copy replacement is used where the constant is applied in the program; with const float MAX = 255; The defined constants hav

of an interesting thing to do, but the way we often use to create objects in object-oriented objects is: Car car=new car (); Using the New keyword is already popular, so we use the above method to define total feeling awkward, and to create new attributes and functions every time we call them, it is not practical. Down we look at the form definition class of the constructor. 2. Constructors This approach looks a bit like a factory function. The s

Definition: The # define Directive You can use the # define directive to give a meaningful name to a constant in your program. The two forms of the syntax are: Syntax # Define identifier token-stringopt # Define identifier [(identifieropt,..., identifieropt)] token-stringopt Usage: 1.SimpleDefineDefinition #

We should be familiar with the span tag, but it is very troublesome to use it, especially when we need to define the width and height for it, html pages often use the span tag, however, some friends may not use this label well. They seem to find it useful, but it is very troublesome to use it, especially when you need to define its width and height. A friend once asked:Why does the width and height of sp

To write a good C language, a beautiful macro definition is very important. Macro definitions can help us prevent errors, improve code portability and readability, and more.In the software development process, there are often common or common functions or code snippets that can be written as functions or encapsulated as macro definitions. So is the function good or the macro definition good? This requires us to make a reasonable choice between the two.Let's look at an example, compare two number

Avascript learn several ways to define objects in JSTransferred from: http://www.cnblogs.com/mengdd/p/3697255.htmlThere is no concept of class in JavaScript, only objects.　　There are several ways to define an object in javascript:1. Extending its properties and methods based on existing objects2. Factory mode3. How to construct a function4. Prototype ("prototype") mode5. Dynamic Prototyping ModeI. Extending

[Conversion] understanding # define sreg (* (volatile unsigned char *) 0x5f)This definition is always very strange. I don't know why. I have a little bit of experience today. Please submit more bricks to the prawns ~~~ Embedded system programming requires programmers to use C language to access a fixed memory address. Since it is an address, according to the syntax rules of the C language, the number of addresses should be pointer type. Therefore, aft

PHP constants: Difference between define and const A constant is the identifier (name) of a simple value ). As its name implies, this value cannot be changed during script execution (except for so-called magic constants, they are actually not constants ). Constants are case sensitive by default. Constant identifiers are always capitalized. You can use the define () function to

After you create a Microsoft SQL Server 2005 Analysis Services (SSAs) project, you can use the project by defining one or more data sources that the project will use. When defining a data source, it defines the connection string information to be used to connect to the data source. For more information, see . In the following tasksAdventureworksdwThe sample database is defined as the data source of the Analysis Services Tutorial Project. For the purpose of this tutorial, the database is loc

Static variables only exist in the function scope. That is to say, static variables only exist in the stack. Generally, variables in a function are released after the function ends, such as local variables, but static variables do not. That is to say, when you call this function again, the value of this variable will be retained. Simplest definition method The define () function defines a constant. Constants are similar to variables, except that: Afte

Title, the implementation of operator+= and operator+ is given below.1sales_data2Sales_data::operator+=(ConstSales_data RHS)3 {4Units_sold + =Rhs.units_sold;5Revenue + =rhs.revenue;6 return* This;7 }8 9 Sales_dataTen operator+(ConstSales_data AMP;LHS,ConstSales_data RHS) One { ASales_data sum = LHS; -sum + = RHS; - returnsum; the}The code above is called operator+ to define the operator+=.First operator+ has two parameters whose parameter type

viewcontroller.m//oc High Efficiency 52 for multiple use type constants, less # define preprocessing directives/*** 1. do not define constants with preprocessing. The defined constants do not contain type information, and the compiler simply performs a find-and-replace operation on this basis before compiling. Immediately someone redefined the constant value, and the compiler does not produce a warning mess

I define a function that accepts the String parameter, but transmits a null value during the call. php will report a fatalerror, but the actual situation will indeed result in a null parameter, I want to define a function that specifies the parameter type and can accept null. what should I do? {Code ...} execute... I define a function that accepts the String para

Recently began preparing for a lab study while documenting some of the programming trivia points encountered. Today when testing the SVD decomposition of matrices, we need to define the size of the rows and columns of the matrix, and I used to define these two variables with a macro definition, and when I run, I start thinking about what the difference between the macro definition and the constant is.Refer

typedef and #define的区别Organized in a classic blog, the classic original address http://www.cnblogs.com/csyisong/archive/2009/01/09/1372363.htmlCase one:In general, typedef are better than # define, especially where pointers are available. Take a look at the example:typedef char *PSTR1;#define PSTR2 char *;PSTR1 S1, S2;PSTR2 S3, S4;In the variable definition above

Both const and # define can be used to define constants in the language, but const has more advantages than # define: (1) const defines constants with data types, while # define does not have data types. The compiler can perform type security checks on the former, while # define