3 ms·

What you would likely do is use an extension bit so there would be no fixed maximum length for the strings. This would of course add a bunch of overhead that yo

What you would likely do is use an extension bit so there would be no fixed maximum length for the strings. This would of course add a bunch of overhead that you may or may not make up with the other advantages of knowing the length of strings.

tptacek 15y ago
This is what DER does to encode ASN.1, and it is basically a nightmare of epic proportions. The 16-bit tag at the beginning of strings is a reasonable suggestion. 65k charstars are slow and unwieldy anyways.
coldnose 15y ago
* If you're appending data to a string, and the variable-length increases by a byte, will you have to memmove() the entire existing string down 1 byte? * Is every programmer responsible for detecting this condition? * (This will make manual string manipulation very complicated and dangerous.) * Suppose you're concatenating two strings, such that the sum of the lengths requires an additional byte. This could cause a buffer overflow. How would a strcat() function avoid causing a buffer overflow here? * Does every string need a maximum-length counter too? * Can you access a random element in the string without having to dereference and decode the length? On the other hand, if you use a constant-sized length, * What happens when you overflow the maximum length? * Can you erroneously create a shorter string by appending text? * How should string libraries handle this condition? By abort()ing? By returning a special error code? Does every string manipulation need to be wrapped in an if() to detect the special error? How should the programmer handle this condition? In either case, * Can you tokenize a string in-place? * Can an attacker read a program's entire address space by finding an address that begins 0xffffffff and treating it as a string?
- spullara 15y ago
  I think most of these are answered with the suggestion that no one would have made strings this way without making a matching library that handled the concerns you have here. Honestly char[] strings are much less useful in a UTF-8 world anyway.

tptacek 15y ago

This is what DER does to encode ASN.1, and it is basically a nightmare of epic proportions. The 16-bit tag at the beginning of strings is a reasonable suggestion. 65k charstars are slow and unwieldy anyways.

coldnose 15y ago

* If you're appending data to a string, and the variable-length increases by a byte, will you have to memmove() the entire existing string down 1 byte? * Is every programmer responsible for detecting this condition? * (This will make manual string manipulation very complicated and dangerous.) * Suppose you're concatenating two strings, such that the sum of the lengths requires an additional byte. This could cause a buffer overflow. How would a strcat() function avoid causing a buffer overflow here? * Does every string need a maximum-length counter too? * Can you access a random element in the string without having to dereference and decode the length? On the other hand, if you use a constant-sized length, * What happens when you overflow the maximum length? * Can you erroneously create a shorter string by appending text? * How should string libraries handle this condition? By abort()ing? By returning a special error code? Does every string manipulation need to be wrapped in an if() to detect the special error? How should the programmer handle this condition? In either case, * Can you tokenize a string in-place? * Can an attacker read a program's entire address space by finding an address that begins 0xffffffff and treating it as a string?

spullara 15y ago
I think most of these are answered with the suggestion that no one would have made strings this way without making a matching library that handled the concerns you have here. Honestly char[] strings are much less useful in a UTF-8 world anyway.