4 ms·

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

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.

AlexanderDhoore 5y ago
Nope, printf can print strings without NULL-terminator: printf("%.*s", <int>length, <char*>string);
- OskarS 5y ago
  And the first argument to printf (the format), what kind of string is that? And what kind of string does sprintf() produce?
  - TazeTSchnitzel 5y ago
    sprintf tells you how many characters it has written, so there's no reason you can't use it for non-null-terminated strings.
    - comfydragon 5y ago
      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.
      - TazeTSchnitzel 5y ago
        Their comment talked about two things, and the sibling comment addressed the other one.
  - 10000truths 5y ago
    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 https://en.wikipedia.org/wiki/Uncontrolled_format_string
  - tialaramex 5y ago
    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.
nicoburns 5y ago
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.
- codesections 5y ago
  > 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/ https://www.joelonsoftware.com/2001/12/11/back-to-basics/
  - slavik81 5y ago
    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 https://godbolt.org/z/Kjh8b44Kf
    - codesections 5y ago
      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?
legulere 5y ago
If you are programming C, you will already roll your own data structures. So why not roll your own formatting routines?

AlexanderDhoore 5y ago

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

OskarS 5y ago
And the first argument to printf (the format), what kind of string is that? And what kind of string does sprintf() produce?
- TazeTSchnitzel 5y ago
  sprintf tells you how many characters it has written, so there's no reason you can't use it for non-null-terminated strings.
  - comfydragon 5y ago
    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.
    - TazeTSchnitzel 5y ago
      Their comment talked about two things, and the sibling comment addressed the other one.
- 10000truths 5y ago
  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 https://en.wikipedia.org/wiki/Uncontrolled_format_string
- tialaramex 5y ago
  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.

nicoburns 5y ago

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.

codesections 5y ago
> 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/ https://www.joelonsoftware.com/2001/12/11/back-to-basics/
- slavik81 5y ago
  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 https://godbolt.org/z/Kjh8b44Kf
  - codesections 5y ago
    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?

legulere 5y ago

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