I quite like being able to generate the same set of pseudo-random data repeatedly, especially with tweaking experimental code. Through observation I would say that rand() seems to give the same sequence of numbers each time*.
Is it guaranteed to do this for repeated executions on the same machine / for different machines / for different architectures?
*For the same seed obviously.
No.
The C standard says:
If srand is then called with the same seed value, the sequence of pseudo-random numbers shall be repeated.
But nowhere does it say what the sequence of pseudo-random numbers actually is - so it differs across implementations.
The only guarantee made is that rand() will give the same sequence of numbers for a given seed for a given implementation. There's no guarantee that the sequence will be the same across different machines or different architectures - and it almost certainly won't be.
If you need to use the exact same set of pseudo-random numbers for experimental purposes, one thing you could do is to use srand to generate a long sequence of random numbers and write them to a file/database. Then, write a portable "random number generator" function that returns values sequentially from that file. That way, you can be assured that you are using the same input data regardless of the platform, srand implementation, or seed value.
When switching to a different machine/runtime/whatever you might be out of luck. There is another possible choice the drand48 family of functions. These are normalized to use the same algorithm on all machines.
It is guaranteed to give the same sequence for the same seed passed to srand() - but only for the duration of a single execution of the program. In general, if an implementation has a choice in behaviour, there is no specific requirement for that choice to remain the same across subsequent executions.
It would be conforming for an implementation to pick a "master seed" at each program startup, and use that to perturb the pseudo-random number generator in a way that is different each time the program starts.
If you wish for more determinism, you should implement a PRNG with specific parameters in your program.