Am 03.12.2013 15:15, schrieb Daniel Lescohier:
A null pointer will cause a segmentation fault. Is it guaranteed that the memory page that the pointer 0xdeadbeef points to is one that is not marked readable & writable, so that one would get a segmentation fault on reading/writing to it?
A null pointer will not cause a segmantation fault on all systems. For example AIX will silently ignore a dereferencing of a null pointer resulting in unexpected behaviour. But your question about 0xdeadbeef is still valid. Its a common practice in memory debugging libraries to mark free'd memory with a pattern which is unlikely a valid pointer. However it depends on the OS and its memory management if 0xdeadbeef is invalid or not. But from my knowledge most OSes uses only the lower half of the address space for user processes.
However, the functions still need to change to return errors for the cases when they are unbuffered files. The buffer won't be referenced (and cause a crash) in those cases.
But in this case the OS will return an EBADF if read() or write() is called.
I think the read/write functions should also do *nbytes=0 when filedes<0 so caller's loops will stop looping. In addition, apr_file_eof should return an error APR_EBADF:
Some sanity checks can help but does not have to... Stefan
