Not including the struct in the header defeats the ability of the user to control where the type is allocated in memory, among other things. That’s a feature th

Not including the struct in the header defeats the ability of the user to control where the type is allocated in memory, among other things. That’s a feature that many c programmers are willing to give up a certain degree of api/abi compatibility for. It’s just a different tradeoff, neither is the best choice in all cases. Of course, if you’re willing to put in a lot of extra legwork, you can do what pthreads does, and define dummy types with the same size for this.