variable-declaration

问题 I had struct errorStruct & a queue errQueue definition in yacc.y , then moved it to separate .h file but it gives me linking error that the definition is found in both yacc.obj and node.obj !! tried creating new solution but still gives the same error Error 9 error LNK2005: "class std::queue<struct errorStruct,class std::deque<struct errorStruct,class std::allocator<struct errorStruct> > > errQueue" (?errQueue@@3V?$queue@UerrorStruct@@V? $deque@UerrorStruct@@V?$allocator@UerrorStruct@@@std@@

问题 What is the difference between declaring an ivar within an @interface versus putting a variable within an @implementation in a .m file? @interface MyClass : NSObject { int num; } - (void)doSomething; @end vs. @implementation MyClass int num2; - (void)doSomething { num = 137; num2 = 138; } @end Is there ever a time when you want to put a variable within the @implementation ? 回答1: The difference between using an ivar and declaring a variable inside the implementation is that the variable within

问题 I saw this declaration in Python, but I don't understand what it means and can't find an explanation: ret, thresh = cv2.threshold(imgray, 127, 255, 0) The question is: why is there there a comma between ret and thresh ? What type of assignment is that? 回答1: That's a "tuple" or "destructuring" assignment - see e.g. Multiple assignment semantics. cv2.threshold returns a tuple containing two values, so it's equivalent to: temp = cv2.threshold(...) ret = temp[0] thresh = temp[1] See Assignment

问题 In my mind, always, definition means storage allocation. In the following code, int i allocates a 4-byte (typically) storage on program stack and bind it to i , and i = 3 assigns 3 to that storage. But because of goto , definition is bypassed which means there is no storage allocated for i . I heard that local variables are allocated either at the entry of the function ( f() in this case) where they reside, or at the point of definition. But either way, how can i be used while it hasn't been

问题 Today I found one interesting thing. I didn't know that one can't declare a variable after a goto label. Compiling the following code #include <stdio.h> int main() { int x = 5; goto JUMP; printf("x is : %d\n",x); JUMP: int a = 0; <=== giving me all sorts of error.. printf("%d",a); } gives errors like temp.c: In function ‘main’: temp.c:7: error: expected expression before ‘int’ temp.c:8: error: ‘a’ undeclared (first use in this function) temp.c:8: error: (Each undeclared identifier is reported

问题 Let we have a Student class. Form the following code snippet (Java) we know - Student aStudent = new Student(); A 'Student' type reference variable is created An object of 'Student' is created with the 'new Student()' The object is assigned with the reference variable 'aStudent' So far I know, each time we write 'new Student()' a new object is created and the newly created object is allocated a memory space. But sometimes we write something like this in a for loop - for ( int i=0; i<10000; i+

问题 Let we have a Student class. Form the following code snippet (Java) we know - Student aStudent = new Student(); A 'Student' type reference variable is created An object of 'Student' is created with the 'new Student()' The object is assigned with the reference variable 'aStudent' So far I know, each time we write 'new Student()' a new object is created and the newly created object is allocated a memory space. But sometimes we write something like this in a for loop - for ( int i=0; i<10000; i+

问题 I have reviewed this but the accepted answer doesn't make sense to me. I should be able to define an enum in C99 as enum WeekDays { MON, TUES, WED, THURS, FRI, SAT, SUN }days; and utilize the enum as follows in main as days = FRI; if (days == FRI) { printf("Thank God it's Friday!"); } Why the additional work in the accepted answer to utilize the enum? 回答1: Your code should work. In general though the accepted answer you point to is better programming practice. It's desirable to separate the

问题 Closed. This question is off-topic. It is not currently accepting answers. Want to improve this question? Update the question so it's on-topic for Stack Overflow. Closed 6 years ago . I've done some searches and couldn't find a list of valid types to use in for loop initialization statements. Is there a fixed list of types that can be used in for loop variable declarations? For instance, consider the following code: for (int i = 0; i < 5; i++) // ... for (String str = "a"; str.length() < 10;

问题 Suppose you have some R object, such data.frame and Quanteda DFM sparse matrix. You want to replicate that object of the same size but no need to copy the content. Is there some R command to replicate any object without copying the content? And if yes, do they work over sparse objects and non-sparse objects? 回答1: this will create the same data structure filled with NA data("iris") iris.mt <- iris[0, ] iris.mt[nrow(iris), ] <- NA str(iris.mt) 'data.frame': 150 obs. of 5 variables: $ Sepal