The const variable specifies whether a variable is modifiable or not. The constant value assigned will be used each time the variable is referenced. The value assigned cannot be modified during program execution. Bjarne Stroustrup’s explanation sums it up briefly: A class is typically declared in a header file and a header file is typically … Read more
When you add the const keyword to a method the this pointer will essentially become a pointer to const object, and you cannot therefore change any member data. (Unless you use mutable, more on that later). The const keyword is part of the functions signature which means that you can implement two similar methods, one … Read more
GCC: pure/const function attributes llvm-gcc: supports the GCC pure/const attributes Clang: seems to support it (I tried on a simple example with the GCC style attributes and it worked.) ICC: seems to adopt the GCC attributes (Sorry, only a forum post.) MSVC: Seems not to support it. (discussion) In general, it seems that almost all … Read more
There are no syntactic differences between C and C++ with regard to const keyword, besides a rather obscure one: in C (since C99) you can declare function parameters as void foo(int a[const]); which is equivalent to void foo(int *const a); declaration. C++ does not support such syntax. Semantic differences exist as well. As @Ben Voigt … Read more
The #define directive is a preprocessor directive; the preprocessor replaces those macros by their body before the compiler even sees it. Think of it as an automatic search and replace of your source code. A const variable declaration declares an actual variable in the language, which you can use… well, like a real variable: take … Read more
In C++, an object is considered fully initialised when execution enters the body of the constructor. You said: “i wanted to know why const must be intialized in constructor initializer list rather than in it’s body ?.” What you are missing is that initialisation happens in the initialisation list, and assignment happens in the body … Read more
Yes — use math.nan. >>> from math import nan >>> print(nan) nan >>> print(nan + 2) nan >>> nan == nan False >>> import math >>> math.isnan(nan) True Before Python 3.5, one could use float(“nan”) (case insensitive). Note that checking to see if two things that are NaN are equal to one another will always … Read more
const char *str in a parameter declaration indicates that the function will not try to modify the values that the str pointer points to. This means that you can call the function with a constant string. If you don’t have const in the declaration, it means that the function might modify the string, so you … Read more
TU A contains the (only) definition of a. So a really is a non-const object, and it can be accessed as such from a function in A with no problems. I’m pretty sure that TU B invokes undefined behavior, since its declaration of a doesn’t agree with the definition. Best quote I’ve found so far … Read more
TL;DR: The 32-bit constant you want to load into x2 is 0xffffffff which corresponds to -1. Since -1 is in the range [-2048, 2047], this constant can be loaded with a single instruction: addi x2, zero, -1. You can also use the li pseudoinstruction: li, x2, -1 which the assembler, in turn, translates to addi … Read more