Outside of any function, int x; is a tentative definition, and some compilers and linkers treat them as a sort of “cooperative definition,” where an identifier can be declared this way in multiple files and will result in defining only one object. C’s rules for external declarations (declarations outside of functions) are a bit complicated … Read more
This behaviour is vexing me time and again. The cause of the trouble is that your A(int n): v(n, A::kDefaultValue) {} odr-uses the static constexpr member, since the constructor of v takes a constant reference second argument. Odr-usage requires a definition somewhere, i.e. const int A::kDefaultValue; in some compilation unit (which is compiled and linked … Read more
The answer depends on what kind of class you’re creating. C++’s compilation model dates back to the days of C, and so its method of importing data from one source file into another is comparatively primitive. The #include directive literally copies the contents of the file you’re including into the source file, then treats the … Read more
Kept having to return here to look up pg_get_viewdef (how to remember that!!), so searched for a more memorable command… and got it: \d+ viewname You can see similar sorts of commands by typing \? at the pgsql command line. Bonus tip: The emacs command sql-postgres makes pgsql a lot more pleasant (edit, copy, paste, … Read more
From JavaScript Closures Two one-sentence summaries: A closure is the local variables for a function – kept alive after the function has returned, or A closure is a stack-frame which is not deallocated when the function returns. (as if a ‘stack-frame’ were malloc’ed instead of being on the stack!) A very good article on closures … Read more
“boilerplate code” is any seemingly repetitive code that shows up again and again in order to get some result that seems like it ought to be much simpler. It’s a subjective definition. The term comes from “boilerplate” in the newspaper industry: wiki
The only use I can think of is to reduce the scope of function declarations: int main() { void doSomething(); doSomething(); return 0; } void otherFunc() { doSomething(); // ERROR, doSomething() not in scope } void doSomething() { … } Of course, there are much better solutions to this. If you need to hide a … Read more
Yes, it’s allowed (§9/2): The class-name is also inserted into the scope of the class itself; this is known as the injected-class-name. For purposes of access checking, the injected-class-name is treated as if it were a public member name. For information about the reasoning that lead to class name inject, you might want to read … Read more
This line of code can probably trigger a vexing (but not “the most vexing”) parse behavior: instead of being interpreted as a variable declaration, it will be interpreted as the declaration of a function named object_name, taking no parameters and returning a value of type class_name. See it happen on GodBolt: The compiler tells you: … Read more
In simple words, a loop invariant is some predicate (condition) that holds for every iteration of the loop. For example, let’s look at a simple for loop that looks like this: int j = 9; for(int i=0; i<10; i++) j–; In this example it is true (for every iteration) that i + j == 9. … Read more