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From: David Brown <david.brown@hesbynett.no>
Newsgroups: comp.lang.c
Subject: Re: relearning C: why does an in-place change to a char* segfault?
Date: Sun, 4 Aug 2024 17:20:42 +0200
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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.