Re: relearning C: why does an in-place change to a char* segfault?

On 04/08/2024 02:07, Keith Thompson wrote:

David Brown <david.brown@hesbynett.no> writes:
[...]

"this is a test" is a string literal, and is typically part of the
program's image.  (There are some C implementations that do things
differently, like storing such initialisation data in a compressed
format.)

[...]
 What implementations do that?  Typically data that's all zeros isn't
stored in the image, but general compression isn't something I've seen
(not that I've paid much attention).  It would save space in the image,
but it would require decompression at load time and wouldn't save any
space at run time.
 

It is a technique I have seen in embedded systems.  It is not uncommon for flash or other non-volatile storage to be significantly slower than ram, and for it to be helpful to keep the flash image as small as possible (this also helps for things like over-the-air updates).  The compression is typically fairly simple, such as run-length encoding, to avoid significant time, code space and temporary ram space, but it can help with some initialised data.