The Define () function defines a constant.define () functions: Defines a constant. Constants is much like variables, except for the following differences: constants [constant] and variables [variable] There are many similarities, so it is easy to confuse; Let's enumerate the differences between constants [constant] and variables [variable]: A constant's value cannot be changed after it is set a constant value cannot be changed after it has been specif
When defining constants in PHP, you can use both the const and define methods, so what's the difference between them?1.const the definition of a class member variable, once defined, cannot be modified. Define is not available for definition of class member variables and can be used for global constants.2.const can be used in a class, define cannot.3.const You can
Define section:Macros can be used not only to replace constant values, but also to replace expressions or even code segments. (Macros have powerful functions but are prone to errors, so their advantages and disadvantages are quite controversial .)
Macro Syntax:# Define macro name macro value
As a suggestion and a common habit of programmers, macro names often use uppercase letters.
Advantages of macros:1)
Difference between const and # define,
(1) Different compiler Processing MethodsThe define macro is expanded in the preprocessing phase.
Const constants are used in the compilation and running phase.
(2) Different Types and security checks
The define macro has no type and does not check any type. It just expands.
Const constants have specific types. during compil
This article mainly introduces how to use mini-define to implement modular management of front-end code. it is a very good article. we recommend it to partners who need it.
Mini-define
A simple front-end modular framework based on require. If you don't want to spend time learning require. js or look at the long cmd/amd specifications, then this mini-define is yo
Correct use of IOS macros (define) and constants (const)In iOS development, macro definitions are often used, or some data types are modified 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 distinguish between the following? Do you know when to use it?#define Hscoder @"Hansha haha"nsstring *hscoder = @
Define section:Macros can be used not only to replace constant values, but also to replace expressions or even code segments. (Macros have powerful functions but are prone to errors, so their advantages and disadvantages are quite controversial .)Macro Syntax:# Define macro name macro valueAs a suggestion and a common habit of programmers, macro names often use uppercase letters.Advantages of macros:1) make
Not only can you define constants in C + + define , but you can also const define constants with the following differences:
A #define MAX 255 defined constant is no type, given an immediate number, the compiler simply links the defined constant value to the name of the defined constant,
Requirejs file Download, select the version you need toRequirejs using instance Step1 to define an HTML fileWe need to define an HTML file named requirehtml.html.Under File content"">"Utf-8"> "Viewport"Content="Width=device-width, initial-scale=1.0"> introduction of require file,../refers to the parent directory of the directory where the current requirehtml.html file resides. Here is the require.js file un
First, the key:1,Inline functions are the same in readability as functions, while at compile time the functions are embedded directly into the body of the caller, eliminating the call/return instruction, which is faster at run time.
2,Inline functions can be debugged, and macro definitions cannot be debugged.
Inline functions and macros are essentially two different concepts if a program writer has a requirement for both fast and readable conditions, the function should be crowned inline. The
Define section:Macros can be used not only in place of constant values, but also in substitution of expressions or even code snippets. (Macros are powerful, but they are also prone to errors, so the pros and cons are quite controversial.) )
The syntax for macros is:#define Macro Name Macro value
As a suggestion and a common habit of programmers, macro names often use all uppercase letters.
Advantages of
#define Aspect_ratio 1.653The compiler will never see aspect_ratio this symbol name, because before the source code into the compiler, it will be removed by the preprocessor, so aspect_ratio will not be added to the list of symbols. If the code involved in this constant is wrong in compiling the times, it can be confusing because the error message refers to 1.653, not aspect_ratio. If Aspect_ratio is not defined in your own header file, you will wonde
The site needs to add a new constant, open the local config.php file, think about the hidef that was tested a few years ago and the APC upgrade define performance.My program has a different configuration for development, testing, production servers, and in constant terms, we use an array that defines all the constants that need to be defined, and then detects if there is a apc_load_constants function, not a batch
typedef and # define are often used to define an alias for an identifier and a keyword, but there are key differences between them.typedef is part of the language compilation process;#define是宏定义语句, it is not in the process of compiling itself, but before the preprocessing process is done.To understand the key differences between the two, you can consider this:See
Http://blog.sina.com.cn/s/blog_686188ef0100klku.html#define是C语言中提供的宏定义命令, the main purpose is to provide programmers with certain convenience in programming, and to a certain extent, improve the efficiency of the program, but students often do not understand the nature of the command in learning, always create some confusion here, in the programming of the misuse of the command, To make the program run inconsistent with the intended purpose, or to rea
#define是C语言中提供的宏定义命令, the main purpose is to provide programmers with certain convenience in programming, and to a certain extent, improve the efficiency of the program, but students often do not understand the nature of the command in learning, always create some confusion here, in the programming of the misuse of the command, To make the program run inconsistent with the intended purpose, or to read the program written by others, the results of the
Let's look at a few examples
(1) struct{int x; int y;} Test1;
Well, define the structure test1,
test1.x and test1.y can be used in the statement.
(2) struct test {int x; int y;} Test1;
Well, define the structure test1,
test1.x and test1.y can be used in the statement. Compared
with 1, the province wrote Test
(3)
typedef struct TEST
{int x; int y;
} TEXT1,TEXT2;
Only said that the structure of the (
When defining constants in PHP, you can use both the const and define methods, so what's the difference between them?1.const the definition of a class member variable , once defined, cannot be modified. Define is not available for definition of class member variables and can be used for global constants .2.const can be used in a class, define cannot .3.const cann
When data is inserted, Oracle considers it as a variable and requires a value.
The reason is that Oracle defines as a custom variable.SQL> show all
Appinfo is off and set to "SQL * Plus"
Arraysize 15
Autocommit off
Autoprint off
Autorecovery off
Autotrace off
Blockterminator "." (hex 2e)
Btitle off and is the first few characters of the next SELECT statement
Eclipsep off
Colsep ""
Compatibility version native
Concat "." (hex 2e)
Copycommit 0
Copytypecheck is on
Read the manual that define defines constants that allow only:
Only scalar and null are allowed. The type of scalar is integer, Float,string, or Boolean. It is also possible to define a constant value of type resource, but it is not recommended to do so, which can lead to the occurrence of an unknown condition.
Read the PHP source code today, found that the second parameter of
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