What are the problems of a zero-terminated string that length-prefixed strings overcome?

Question

What are the problems of a zero-terminated string that length-prefixed strings overcome?

I was reading the book Write Great Code vol. 1 and I had that question in mind.<

Answer 1

A few more bonus features that can be implemented with length-prefixed strings:

1. It's possible to have multiple styles of length prefix, identifiable through one or more bits of the first byte identified by the string pointer/reference. In exchange for a little extra time determining string length, one could e.g. use a single-byte prefix for short strings and longer prefixes for longer strings. If one uses a lot of 1-3 byte strings that could save more than 50% on overall memory consumption for such strings compared with using a fixed four-byte prefix; such a format could also accommodate strings whose length exceeded the range of 32-bit integers.

2. One may store variable-length strings within bounds-checked buffers at a cost of only one or two bits in the length prefix. The number N combined with the other bits would indicate one of three things:

   1. An N-byte string

   2. (Optional) An N-byte buffer holding a zero-length string

   3. An N-byte buffer which, if its last byte B is less than 248, holds a string of length N-B-1; if the 248 or more, the preceding B-247 bytes would store the difference between the buffer size and the string length. Note that if the length of the string is precisely N-1, the string will be followed by a NUL byte, and if it's less than that the byte following the string will be unused and could be set to NUL.

   Using such an approach, one would need to initialize strong buffers before use (to indicate their length), but would then no longer need to pass the length of a string buffer to a routine that was going to store data there.

3. One may use certain prefix values to indicate various special things. For example, one may have a prefix that indicates that it is not followed by a string, but rather by a string-data pointer and two integers giving buffer size and current length. If methods that operate on strings call a method to get the data pointer, buffer size, and length, one may pass such a method a reference to a portion of a string cheaply provided that the string itself will outlive the method call.

4. One may extend the above feature with a bit to indicate that the string data is in a region that was generated by malloc and may be resized if needed; additionally, one could safely have methods that sometimes return a dynamically-generated string allocated on the heap, and sometimes return an immutable static string, and have the recipient perform a "free this string if it isn't static".

I don't know if any prefixed-string implementations implement all those bonus features, but they can all be accommodated for very little cost in storage space, relatively little cost in code, and less cost in time than would be required to use NUL-terminated strings whose length was neither known nor short.