declaration

问题 I am using a library that consists almost entirely of templated classes and functions in header files , like this: // foo.h template<class T> class Foo { Foo(){} void computeXYZ() { /* heavy code */ } }; template<class T> void processFoo(const Foo<T>& foo) { /* more heavy code */ } Now this is bad because compile times are unbearable whenever I include one of those header files (and actually I include many of them in each of my compilation units). Since as a template parameter I only use one

问题 I'm reading 'The C Programming Language' and encountered a problem about typedef of struct . The code is like this: typedef struct tnode *Treeptr; typedef struct tnode { /* the tree node: */ char *word; /* points to the text */ int count; /* number of occurrences */ struct tnode *left; /* left child */ struct tnode *right; /* right child */ } Treenode; By the time we write typedef struct tnode *Treeptr; tnode is still not declared yet, but we don't get any compilation error, but when we

问题 I'm reading 'The C Programming Language' and encountered a problem about typedef of struct . The code is like this: typedef struct tnode *Treeptr; typedef struct tnode { /* the tree node: */ char *word; /* points to the text */ int count; /* number of occurrences */ struct tnode *left; /* left child */ struct tnode *right; /* right child */ } Treenode; By the time we write typedef struct tnode *Treeptr; tnode is still not declared yet, but we don't get any compilation error, but when we

问题 I was reviewing someone else's code the other day and I came across a line that raised some concern. To simplify, say I have a generic Class A and an abstract Class B. Is the following instantiation allowed and if so, why? Object obj = new A<? extends B>(); I personally have never seen an instantiation like the above, although a declaration such as A<? extends B> obj = null; would certainly hold. I've always used the wildcard in generics to declare method parameters, so I may just not have

问题 This question already has answers here : Multiple assignment in javascript? What does [a,b,c] = [1, 2, 3]; mean? (4 answers) Closed 2 years ago . Take the following line of code const [component] = router.getMatchedComponents({ ...to }) Could anyone advise what the square brackets around component means here? I have tried to google this but struggling to find an answer 回答1: It's called Destructuring assignment, and it's used to unpack the values of an array and assign them to new variables.

问题 When I was first introduced to C I was told to always declare my variables at the top of the function. Now that I have a strong grasp of the language I am focusing my efforts on coding style, particularly limiting the scope of my variables. I have read about the benefits to limiting the scope and I came across an interesting example. Apparently, C99 allows you to do this... for (int i = 0; i < 10; i++) { puts("hello"); } I had thought that a variables scope was limited by the inner-most

问题 In Why can't you declare a variable inside a do while loop? the OP asks why a declaration in the while-condition of a do-while loop isn't in scope in the do-statement. That would be very unnatural as C/C++ generally follow a "declaration-at-top-of-scope" pattern. But what about the converse - why not extend the scope of any declaration in the do-statement to the while-condition. That would allow int i; do { i = get_data(); // whatever you want to do with i; } while (i != 0); to be shortened

问题 I found this line in stdio.h : extern struct _IO_FILE *stdin; Based on this 'extern' keyword, i assume this is just a declaration. I wonder where is stdin defined and initialized? 回答1: It's defined in the source code of your C library. You typically only need the headers for compilation, but you can find the source code for many open-source standard libraries (like glibc). In glibc, it's defined in libio/stdio.c as like this: _IO_FILE *stdin = (FILE *) &_IO_2_1_stdin_; Which is in turn

问题 I am new to iphone development, Now i want to access the string variable in all the view controller, but i know to declare the variables in delegate method, but i cant access it, please help me out. Mainviewcontroller-->Viewcontroller1_-->viewcontroller2-->viewcontroller3-->subwebview. i have created one main view controller and the subview class are Viewcontroller1,viewcontroller2,viewcontroller3. And the subwebview is the subclass of all the three viewcontrollers(Viewcontroller1

问题 In implementing an interface it seems the common method in tutorials and literature is to declare an ivar and then set the @property then @synthesize . @interface MyClass : NSObject { NSString *myString; } @property (nonatomic, retain) NSString *myString; @end However, omitting the explicit declaration and just putting @property has the same effect. @interface MyClass: NSObject { } @property (nonatomic, retain) NSString *myString; @end So how come most people use @property and an explicit