(1)
"/" And a macro with a long number of rowsThe macro definition can contain more than two lines of commands. In this case, you must add "/" on the rightmost side and the line "/". No more characters are allowed, and no comments are allowed, the following line must end with "/", "/" followed by a space, and an error will be reported, not to mention it.# Define Exchange (a, B ){/Int t ;/T = ;/A = B ;/B = T ;/}
(2)
'/' And a long condition judgment st
Define constant. According to the manual, only constants defined by define are allowed: scalar and null. The scalar type is integer, float, string, or boolean. You can also define the constant value type as resource. see the manual. the constants defined by define are only allowed:
Only scalar and null are allowed.
Constant:
Representing constants with macros
If we want to write a program for various computation of circles, then the round (3.14159) value will be widely used. We obviously have no reason to change the value of limit, so we should treat it as a constant. So, do we have to write the 3.14159 long string over and over again? The macro is used. Macros can be used not only to replace constant values, but also to replace expressions or even code segments. Macro Syntax:
#
1) # define is a pre-processing command. It is a simple replacement during compilation and pre-processing, and does not check the correctness. It does not mean that it is correct or not, possible errors are detected and reported only when the expanded source program is compiled. For example:# Define PI 3.1415926In the program: Area = pI * r will be replaced with 3.1415926 * r * RIf you write the number 9 in
it must have been seen by many people. #ifndef/#define/#endif in the header file prevents the header file from being repeatedly referenced. But what does it mean to understand "repeated references"? Is it possible to include this header file in a different two files using include? What happens if the header file is repeatedly referenced? Are all header files to be added to #ifndef/#define/#endif these codes
lifestyle.But it's not enough to just give the answer above. I believe we are still waiting for my explanation: physiological reasons? You're not kidding me!I'm not joking. In fact, simply explaining "physical causes" is not enough. To make this answer truly perfect, we have to explain two big questions:Question 1: By what definition: this group because of physiological factors and extremely pay attention to Chichuanyongdu people, is the upper class society. What other people say is not. Can't
typedef :If 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.Such as:typedef ...//Start here to end of file#
Everyone should know that define and const are constants in PHP, so how much do you know about them? This article mainly and everyone to share PHP define and the difference between the const detailed, hope to help everyone.
The understanding of constants:
The constant is preceded by a dollar sign ($);
Constants can only be defined with the Define () functi
How does the define constant prevent the address bar from directly accessing the background file? define cannot be cross-page, but recently it was like this in an open source PHP Project: for example,. php: define (IN_TM, TRUE); B. php direct lt ;? Phpif (! Defined (IN_TM) {exit (AccessDenied) ;}if ($ _ SESSION [ quot; admi
Define () function understanding 1 (focusing on the understanding of the function)The Define () function defines a constant.Characteristics of constants:Constants are similar to variables, except that, after setting, the value of a constant cannot change the constant name, does not require a dollar sign ($) at the beginning, and the scope does not affect access to the constant, which can only be a string or
This article really does not have any difficulty, I am in order to test my English level degenerated not haha although my English originally had the dregs to translate also like plain English. Will read the original version of the code after the translation of almost one hours, in which the comments are part of their own understanding of the omission or misunderstanding is also grateful to the place, such as JavaScript in the understanding of a single example of the sense of the definition of a
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 = @ "Hansha haha";extern NSString *hscoder;extern const NSString *hscoder;static const NSString *hscoder
In C + +, we can define the so-called symbolic constants by #define This instruction, which is directly compiled into binary code. In this case, it is basically the same as the effect of the constant value variable defined with Const. Of
For example:
But #define also has the function of changing compiler behavior, for example, depending on whether or not yo
1. Define a simple constant: Define a constant to facilitate modification. (do not add a semicolon to the end !)
# Define n 1000
It is equivalent to const int n = 1000, but slightly different. Define is a simple replacement instead of a quantity.
2. Define simple functions:
1. Simple define Definition# Define maxtime1000A simple maxtime is defined. It represents 1000. If you writeIf (I The compiler replaces maxtime with 1000 before processing this code.This definition looks similar to a normal constant definition const, but it is also different, because the definition of define is more like a simple text replacement, rather than bei
Original article address:
Http://blog.csdn.net/kindazrael/article/details/8108868
Objective-C: # define Usage Analysis
In C, Preprocessor is a powerful tool that makes your code easier to read and modify. With preprocessing code, you can redefine a part of the code to make your code more suitable for your style. Preprocessor is processed in advance before the code is compiled. The pre-processing code starts with a pound sign.1. About
#
There is a constant DATA_PATH, and a string quot; file_name quot; how to define a variable in the class (the constant seems to need 5.7), which indicates DATA_PATH and quot; file_name quot;. I can define it outside the class as follows: {code ...} but it won't work in the class: {code ...}... there is a constant DATA_PATH and a string "file_name"
How to define
(1) different compiler processing methodsDefine macros are expanded during the preprocessing phase.Const constants are used during the compile run phase.(2) Different types and security checksDefine macros have no type, do not do any type checking, just expand.Const constants have specific types that perform type checking during the compilation phase.(3) different storage methodsThe Define macro is only expanded, how many places are used, how many tim
Static
I. backgroundCause: when the program executes the variable defined in the function to its definition, the compiler allocates space for it on the stack, the space allocated by the function on the stack is released at the end of the function execution. This creates a problem: If you want to save the value of this variable in the function to the next call, how to implement it?The easiest way to think of is to define a global variable, but defining
I. Usage of typedef:
①Define a type of Alias, not just a simple macro replacement. It can be used to declare multiple objects of the pointer type at the same time. Trap: typedef char * tchar;
Tchar Pa, PB; // Pa and Pb are pointer types. # Define cannot achieve this effect.
Trap: typedef char * pstr;
Int mystrcmp (const pstr, const pstr); const pstr is equivalent to char? No, it is actually equivalent to ch
The content source of this page is from Internet, which doesn't represent Alibaba Cloud's opinion;
products and services mentioned on that page don't have any relationship with Alibaba Cloud. If the
content of the page makes you feel confusing, please write us an email, we will handle the problem
within 5 days after receiving your email.
If you find any instances of plagiarism from the community, please send an email to:
info-contact@alibabacloud.com
and provide relevant evidence. A staff member will contact you within 5 working days.