Quentin Pope said:
What is the principle difference between a Bus Error and a Segmentation
Fault please.
It's implementation-specific. Not all implementations have
either one.
The glibc manual describes one common distinction:
-- Macro: int SIGSEGV
This signal is generated when a program tries to read or write
outside the memory that is allocated for it, or to write memory
that can only be read. (Actually, the signals only occur when the
program goes far enough outside to be detected by the system's
memory protection mechanism.) The name is an abbreviation for
"segmentation violation".
Common ways of getting a `SIGSEGV' condition include dereferencing
a null or uninitialized pointer, or when you use a pointer to step
through an array, but fail to check for the end of the array. It
varies among systems whether dereferencing a null pointer generates
`SIGSEGV' or `SIGBUS'.
-- Macro: int SIGBUS
This signal is generated when an invalid pointer is dereferenced.
Like `SIGSEGV', this signal is typically the result of
dereferencing an uninitialized pointer. The difference between
the two is that `SIGSEGV' indicates an invalid access to valid
memory, while `SIGBUS' indicates an access to an invalid address.
In particular, `SIGBUS' signals often result from dereferencing a
misaligned pointer, such as referring to a four-word integer at an
address not divisible by four. (Each kind of computer has its own
requirements for address alignment.)
The name of this signal is an abbreviation for "bus error".