Willy, Am 05.03.20 um 19:40 schrieb Willy Tarreau: > Don't worry, it's not a matter of C experience or whatever. C isn't trivial > and we all have doubts about plenty of things. Some people put tons of > parenthesis because operators precedence is never obvious, others have > trouble with const, others with many other things. And in the end they > still produce good code that runs the whole internet because they're > careful. > > Regarding the "const" thing, I can give you a few hints if that helps. > The first one is to remember that when you write: > > type *pointer; > > it means "*pointer is of type <type>" thus "pointer is a pointer to an > area of type <type>". So when you write "const char *pointer", then > "pointer is a pointer to an area of const char".
Yeah, I technically know this, but `const char *` reads to me like "const (char pointer)" not "(const char) pointer" :-) > Another way to remind it is that when you write strings in your code > like: > > p = "alalafred"; > > Then this string in quotes is a const. And it's for this that you > generally want to place "const char *" in front of the argument of a > function that it supposed to support such an argument which must not > be modified. Thus strlen() takes a const char *, in order to be > compatible with this. Yes, the bit about const chars makes sense. I guess I can remember that (I hope). > One tricky area is related to allocations. You could think that it'd > be fine to set the return of an strdup() to "const char*" because you > don't need to modify it. But there's a catch. Whatever is before or > after the area belongs to the area, and free() will need to modify > some hidden pointers around this, or even inside the area. Thus free() > cannot take a "const void*", and it will need a "void*". For this > reason, when you copy the result of an strdup() into a variable that > you don't intend to modify, you still need to declare it as a pointer > to a writable area just so that free() can be called on it upon exit. Oh, this is good to know. I wasn't aware of that. Thanks Tim Düsterhus
