alt Hacker NewsThe size overhead of that is 2*sizeof(int) while the overhead of null termination is sizeof(char). If I remember the standard right, the former is worse by at least sizeof(char), and usually more in practice. This used to matter, sometimes still does.
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Well, not saying to always use it, but if the string size is big enough, the overhead of 2 ints becomes relatively vanishing. For generic dynamically sized strings it probably has more advantages than disadvantages. But in any case, sure, if every single byte matters or some structure requires specific memory layout, then fine. I just don't think these things are the majority of use cases. Keep in mind that the cached lengths can increase performance, since you don't have to recalculate string lengths.
I would assume the difference is mostly negligible in practice due to the allocator rounding up the allocated memory size at least by the word size anyway (for alignment and simpler bookkeeping). You can also use variable-length encoding in the header to use 1 byte for most cases, similar to how UTF-8 does it: if the most significant bit is not set, we assume a 7-bit encoding, which can represent string lengths up to 127 using 1 byte, which is probably 99% of strings.