Oh yes, totally undefined. But consider the time frame, early 1980s K&R C on 4bsd Unix on a VAX. This predates ANSI/ISO C and Posix. It even predates “nasal de

Oh yes, totally undefined. But consider the time frame, early 1980s K&R C on 4bsd Unix on a VAX. This predates ANSI/ISO C and Posix. It even predates “nasal demons.” There was no specification; or perhaps the implementation was the specification. The fact was that at some point the bsd allocator did leave freed memory untouched until the next memory allocation operation, and so people wrote programs that relied on this. Again, I’m not defending this, but this seemed to be the way that some people thought about things. I even remember questioning some code that used memory after having freed it. It was explained to me that this was “safe” because the memory wouldn’t be modified until the next malloc! Also, remember that BSD was the system where if you did printf("%s", NULL); it would print “(null)” instead of getting SIGSEGV. And in general, deferencing a null pointer would return zero. The rationale for this was that it “made programs more robust.” (Again, I disagree, don’t argue with me about this!) One more common technique from the BSD era (srogue again, but other programs did this too). To save the state of a program, write to a file everything between the base of the data segment to the “break” at the top of the data segment. To restore, just sbrk() to the right size and read it all back in, overwriting everything starting at the base of the data segment. I always found it surprising that this worked, but it worked often enough that people did sh!t like this.