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Comment by cperciva | Hacker News Reader

Now that I understand what you're saying: This is one of the reasons I hate the "feature" in C++ and C99 that you can declare variables anywhere. If you stick to declaring all your variables in one place, it's much easier to notice when you've already used a variable name.

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And much easier to wind up with lots of bad dead code or worse, reusing variables over and over leading to tightly coupled code. IMHO, variables should be declared as closely as possible to where they're used in the smallest scope possible. C languages do it right.

Have you tried the GCC -Wshadow warning flag? It will generate a warning whenever you define a variable with the same name as one declared in an outer scope.

Between that, and using -Werror to ensure that warnings never get ignored, I find C99-style declare-anywhere quite useful. It helps me keep the scope of variables limited to the places that need them.

That said, I rarely use C99's ability to declare a variable in the middle of a block. I primarily use the C99 feature of declaring variables as part of a loop.

(I'm no C expert, I'm posting my take on this mainly because I'm interested in learning from counterarguments):

Greatgrandparent's error was lack of such inner declaration. -Wshadow wouldn't help with that.

Also, I imagine enforcing old-style declaration restrictions helps you to avoid introducing those errors in first place, but it's just as hard to debug them once they're in.

My choice would be to get in the habit of declaring a variable in the narrowest scope that makes sense. I can't see much of a problem with this (esp. in the context of C!) barring old habit. I don't think Scheme programmers, for example, have this stuff any easier and I don't think scoping is perceived as a problem there.

I agree with you entirely that -Wshadow (or an equivalent for JavaScript) would not solve the problem reported in the original article. However, it does solve the problem cperciva mentioned in the comment I replied to: "If you stick to declaring all your variables in one place, it's much easier to notice when you've already used a variable name.". -Wshadow detects when you've already used a variable name and reports that as a warning (or an error if you use -Werror, which you should).

I also agree about declaring a variable in the narrowest scope that makes sense. I often see code that attempts to reuse the same variable for several different purposes, rather than declaring separate variables in narrower scopes.

Umm, I find the opposite to be true. By always declaring variables where I use them (notably in for loops), I avoid accidentally reusing a variable I used elsewhere.

That is a special case. Loop headers should be considered the top of scope blocks in C. I don't know why the language designers didn't do that.

They did, in C99.

That makes variables scope over far more than they need to, opening up a pretty frequent bug avenue of using the wrong variable that you did not intend to use.

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