Antirez/sds: Simple Dynamic Strings library for C

Summary

Simple Dynamic Strings Notes about version 2: this is an updated version of SDS in an attempt to finally unify Redis, Disque, Hiredis, and the stand alone SDS versions. This version is NOT binary compatible* with SDS verison 1, but the API is 99% compatible so switching to the new lib should be trivial. Note that this version of SDS may be a slower with certain workloads, but uses less memory compared to V1 since header size is dynamic and depends to the string to alloc. Moreover it includes a few more API functions, notably sdscatfmt which is a faster version of sdscatprintf that can be used for the simpler cases in order to avoid the libc printf family functions performance penalty. How SDS strings work SDS is a string library for C designed to augment the limited libc string handling functionalities by adding heap allocated strings that are: Simpler to use. Binary safe. Computationally more efficient. But yet... Compatible with normal C string functions. This is achieved using an alternative design in which instead of using a C structure to represent a string, we use a binary prefix that is stored before the actual pointer to the string that is returned by SDS to the user. +--------+-------------------------------+-----------+ | Header | Binary safe C alike string... | Null term | +--------+-------------------------------+-----------+ | `-> Pointer returned to the user. Because of meta data stored before the actual returned pointer as a prefix, and because of every SDS string implicitly adding a null term at the end of the string regardless of the actual content of the string, SDS strings work well together with C strings and the user is free to use them interchangeably with other std C string functions that access the string in read-only. SDS was a C string I developed in the past for my everyday C programming needs, later it was moved into Redis where it is used extensively and where it was modified in order to be suitable for high performance operations. Now i...