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Comment by williamvds | Hacker News Reader

Unfortunately C is locked into null-terminated strings, given that all the printf-style functions work on the assumption there'll be a null terminator. C++ has std::string_view which is pointer + length, but you've still got the same problem if you need to call older printf-style functions.

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Why do you have to use printf? You could have a string library would could with it's own formatting routines. There's also the option of using both a length AND a null terminator.

> There's also the option of using both a length AND a null terminator.

I first encountered that idea in this classic Joel on Software post, which rather put me off the idea of using them in production:

> Notice in this case you’ve got a string that is null terminated (the compiler did that) as well as a Pascal string. I used to call these fucked strings because it’s easier than calling them null terminated pascal strings but this is a rated-G channel so you will have use the longer name.

https://www.joelonsoftware.com/2001/12/11/back-to-basics/

Joel's article is a bit long in the tooth. As of C++11, std::string is required to use both a length and a null terminator. With the short string optimization, it could even have that exact layout.

> Lazy programmers would do this, and have slow programs

    char* str = "*Hello!";
    str[0] = strlen(str) - 1;

Modern compilers understand strlen, and will replace the function call with a constant where possible. That code's not slow anymore: https://godbolt.org/z/Kjh8b44Kf

That's good to know, thanks.

But Joel was talking about C rather than C++, where your comments about std::string wouldn't apply, right?

If you are programming C, you will already roll your own data structures. So why not roll your own formatting routines?

Nope, printf can print strings without NULL-terminator: printf("%.*s", <int>length, <char*>string);

And the first argument to printf (the format), what kind of string is that? And what kind of string does sprintf() produce?

In practice, it is almost always a compile-time-known string. gcc will warn you if it isn't, especially since allowing the use of untrusted input for the format can lead to vulnerabilities:

https://en.wikipedia.org/wiki/Uncontrolled_format_string

Anywhere that this format is a variable, you probably already screwed up. C allows that, but if I see it that's getting flagged in my review.

So long as the format string is a literal you needn't care how it works.

Now, one of the places where C makes this nastier than it needed to be is that C built-in types are silly, and so any non-trivial program is using better fundamental types like uint32_t (or the more succinct u32), for which the built-in formatter offers no syntax. So you end up writing format strings like "There are "PRIu32" dogs\n" using macros to bring in the appropriate specifier for your literal. Blergh.

sprintf tells you how many characters it has written, so there's no reason you can't use it for non-null-terminated strings.

williamvds's point is that the first argument to printf is still itself a null-terminated string, so it's basically turtles all the way down if you're using the C standard library.

Their comment talked about two things, and the sibling comment addressed the other one.

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