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Comment by nerdponx | Hacker News Reader

assignments inside a conditional check

I see this in C code often. Why do people seem to like doing this?

As demonstrated by other commenters, makes for a terse iterator-ish pattern in languages without iterators (like C, or until recently Javascript) e.g.

    while ((c = getchar()) != EOF) {
     //
    }

in a language with iterators would be

    for (c in chars()) {
     //
    }

And note that this C pattern only works when you can pass the "end of iteration" signal in-band, if you can't you will need to use more complex pseudo-iteration protocols e.g.

    while(generator(&c)) {
        //
    }

Because

    while ((c = getchar()) != EOF) {
     //
    }

Is considered more idiomatic and readable than any alternatives that's not assigning to c within the conditional. You'll see similar idioms in many other languages, e.g.

     while((line = reader.readLine()) != null) {
     }

But if you're talking about e.g.

    if (foo = (bar & 0xf)) {
    }

It's just bad style ...

I think it's more idiomatic because otherwise you have to do:

  char c = EOF;
  while (c != EOF) {
    c = getchar();
    ...
  }

The idiomatic way reads better: "while next character is not EOF".

Your (excellent) example of bad style is bad because it reads poorly: "if the result of the assignment of bar & 0xf to foo is true". Not only that, but it is not obvious what the result of an assignment is, if anything. (Yes, I do know it is the value, but personally, I think <nothing> is a more logical result).

Don't you mean

    char c = getchar();
    while (c != EOF) {
        c = getchar();
        …
    }

Which not only reads badly but requires writing the "producer" twice. Though alternatively you could:

    while (1) {
        c = getchar();
        if (c == EOF) { break; }
        ...
    }

    char c;
    do {
        c = getchar();
    } while (c != EOF);

This is worse, in most cases as you normally want to do something to c after you have read it, forcing you to re-check the condition

    int c; //a char can't represent EOF
    do {
        c = getchar();
        if (c != EOF) {
           //do stuff
        }
    } while (c != EOF);

if ((err = func())) goto fail_err;

Two of the most hated thing of C but so convenient...

Masochism?

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