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What this means is actually equivalent to the fact that you can replace the preprocessor with a compiler.Because using a preprocessor may make it impossible for the processed things to enter the symbol table, for example #define MaxLen 16 Here The MaxLen does not enter the symbol table, so there is a compile error when the prompt is 16 instead of MaxLen, which brings a lot of errors. For the above formula, you can try to use a constant to replace the

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

Const and define all define constants in PHP, but what are their specific differences? In fact, very simple const is used for the definition of a class member variable, once defined and cannot change its value. Define defines a global constant that can be accessed anywhere the page define cannot be defined in the class

C # preprocessor directives are never translated into executable code commands, but can affect all aspects of the compilation process, common preprocessor directives have # define, #undef, #if, #elif, #else和 #endif, and so on, the following describes C # use # Define an instance of conditional compilation.In C #, conditional compilation directives are used to conditionally include or exclude portions of a s

# DefineCreate a macro that is an identifier or parameterized identifier associated with the tag string. After defining the macro, the compiler can mark a string to replace each matching item of the identifier in the source file.Syntax # DefineIdentifierToken-string # DefineIdentifier(Identifier1,...,IdentifierN)Token-stringRemarks 1 # defineCommand to enable the CompilerToken-stringReplacing the source fileIdentifier. Only whenIdentifierIt is replaced only when a tag is formed. That is to say,

Usage of "#" and "#" in macroI. general usageWe use # to convert the macro parameter into a string, and # to combine the two macro parameters.Usage:# Include# IncludeUsing namespace STD; # Define STR (s) # s# Define cons (a, B) int (A ## e ## B) Int main (){Printf (STR (vck); // output string "vck"Printf ("% d/N", cons (2000); // 2e3 output:Return 0;} 2. When the macro parameter is another macroIt should be

A constant is a simple identifier. This value cannot be changed during script execution (in addition to the so-called magic constants, they are not constants). Constants are case sensitive by default. Usually, constant identifiers are always uppercase.You can use the Define () function to define constants. After php5.3.0, you can use the Const keyword to define c

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

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