lvalue

In R, "assign('x',v)" sets the object whose name is 'x' to v. Replace 'x' by the result of applying a text function to a variable x. Then "assign" shows its worth. Unfortunately, "assign(paste('names(','x',')',sep=''),v)" fails. So if 'x' is a variable x, I can set its value, but I can't give it names for its elements. Can one work around this? a parse-eval trick maybe? Thanks. In the form you ask question there is no need to assign names. If you x exists then you do names(x) <- v . This is right way to do this. If your variable name is unknown (i.e. dynamically created) then you could use

What i think is that dynamic type means dynamically allocated object using new . In the following case, do you say p points to dynamic type or static type of object? In standard, it doesn't say about dynamic type being dynamic object. 1.3.3 - The type of the most derived object (1.8) to which the lvalue denoted by an lvalue expression refers. [Example: if a pointer (8.3.1) p whose static type is "pointer to class B" is pointing to an object of class D, derived from B (clause 10), the dynamic type of the expression *p is "D." References (8.3.2) are treated similarly. ] Also what does it the

In C++, pre-increment operator gives lvalue because incremented object itself is returned, not a copy. But in C, it gives rvalue. Why? C doesn't have references. In C++ ++i returns a reference to i (lvalue) whereas in C it returns a copy(incremented). C99 6.5.3.1/2 The value of the operand of the prefix ++ operator is incremented. The result is the new value of the operand after incrementation . The expression ++Eis equivalent to (E+=1). ‘‘value of an expression’’ <=> rvalue However for historical reasons I think "references not being part of C" could be a possible reason. Nawaz C99 says in the

I am trying to understand how pointer incrementing and dereferencing go together, and I did this to try it out: #include <stdio.h> int main(int argc, char *argv[]) { char *words[] = {"word1","word2"}; printf("%p\n",words); printf("%s\n",*words++); printf("%p\n",words); return 0; } I expected this code to do one of these: First dereference then increase the pointer (printing word1) First dereference then increase the value (printing ord1) Dereference pointer + 1 (printing word2) But compiler won't even compile this, and gives this error: lvalue required as increment operand am I doing something

I've been reading quite many on the Internet and it seems that many people mentioned the following rules (but i couldn't find it in the standard), The addition operator + (and all other binary operators) requires both operands to be rvalue, and the result is rvalue. And so on.. I checked the C++ standard, and it clearly states that (clause 3.10/2), Whenever a glvalue appears in a context where a prvalue is expected, the glvalue is converted to a prvalue (clause 5/9), Whenever a glvalue expression appears as an operand of an operator that expects a prvalue for that operand, the lvalue-to-rvalue