static-variables | 易学教程

Calling some functions before main in C

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问题 I'd like to do some stuffs before main function. I have multiple source files. In each file, there is some work that needs to be done before main . It was no problem in C++, but problematic with C. In C++, this can be done by two ways: Exploiting a constructor of a global class/struct. Calling a function to a global variable For example, static const int __register_dummy_ = __AddRegisterMetaInfo(...); However, in C, either ways is impossible. Obviously, there is no constructor. So, the first

When should I use static methods in a class and what are the benefits?

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I have concept of static variables but what are the benefits of static methods in a class. I have worked on some projects but I did not make a method static. Whenever I need to call a method of a class, I create an object of that class and call the desired method. Q: Static variable in a method holds it's value even when method is executed but accessible only in its containing method but what is the best definition of static method? Q: Is calling the static method without creating object of that class is the only benefit of static method? Q: What is the accessible range for static method?

Local variables set to nil? (Objective-C)

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问题 I'm reading a book on Objective-C and the author said that if local variables aren't assigned a value they will be set to nil, but static variables will be set to zero. So, I set up int a and didn't assign it a value. Then NSLog(@"%i", a) to display it and a was displayed as zero. I was a little confused on that and I was wondering if someone could clarify it for me? 回答1: With ARC enabled, your Objective-C object pointer variables will be set to nil regardless of where you create them.

Values obtained in case of a recursive function

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问题 Can anyone explain to me the reason behind the output of this program to be 0 0 0 0 0 ? Here we are using a static variable var whose values will not change due to function calls. The values of var will be 4, 3, 2, 1 during the recursive calls. When var becomes zero the recursion terminates and control moves on to the printf statement. Why is the output not 1,2,3,4 ? main(){ static int var=5; if(--var) main(); printf(" %d ",var); } Again if you use if condition var-- then program output will

How do I declare a static variable inside the Main method?

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问题 Can we declare Static Variables inside Main method? Because I am getting an error message: Illegal Start of Expression 回答1: Obviously, no, we can't. In Java, static means that it's a variable/method of a class, it belongs to the whole class but not to one of its certain objects. This means that static keyword can be used only in a 'class scope' i.e. it doesn't have any sense inside methods. 回答2: You can use static variables inside your main method (or any other method), but you need to

Static Variables in R

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问题 I have a function in R that I call multiple times. I want to keep track of the number of times that I've called it and use that to make decisions on what to do inside of the function. Here's what I have right now: f = function( x ) { count <<- count + 1 return( mean(x) ) } count = 1 numbers = rnorm( n = 100, mean = 0, sd = 1 ) for ( x in seq(1,100) ) { mean = f( numbers ) print( count ) } I don't like that I have to declare the variable count outside the scope of the function. In C or C++ I

Static vs Instance Variables: Difference?

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What is the difference between a static and instance variable. The following sentence is what I cant get: In certain cases, only one copy of a particular variable should be shared by all objects of a class- here a static variable is used. A static variable represents class wide info.All objects of a class share the same data. I thought that instance vars were used class wide whereas static variables only had scope within their own methods? In the context of class attributes, static has a different meaning. If you have a field like: private static int sharedAttribute; then, each and every

C++ static member variable and its initialization

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For static member variables in C++ class - the initialization is done outside the class. I wonder why? Any logical reasoning/constraint for this? Or is it purely legacy implementation - which the standard does not want to correct? I think having initialization in the class is more "intuitive" and less confusing.It also gives the sense of both static and global-ness of the variable. For example if you see the static const member. John Dibling Fundamentally this is because static members must be defined in exactly one translation unit, in order to not violate the One-Definition Rule . If the

Access a global static variable from another file in C

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问题 In C language, I want to access a global static variable outside the scope of the file. Let me know the best possible way to do it. One of the methods is to assign an extern global variable the value of static variable, In file a.c static int val = 10; globalvar = val; In file b.c extern globalvar; But in this case any changes in val(file a.c) will not be updated in globalvar in (file b.c). Please let me know how can I achieve the same. Thanks, Sikandar. 回答1: Well, if you can modify file a.c

When should I use static methods in a class and what are the benefits?

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问题 I have concept of static variables but what are the benefits of static methods in a class. I have worked on some projects but I did not make a method static. Whenever I need to call a method of a class, I create an object of that class and call the desired method. Q: Static variable in a method holds it\'s value even when method is executed but accessible only in its containing method but what is the best definition of static method? Q: Is calling the static method without creating object of