Experimental Physics and Industrial Control System
Hi:
On Jul 27, 2005, at 12:15, Andrew Johnson wrote:
I am considering an implementation of variable length strings that
does not require the reallocation and copying of data as the string is
extended. This would use a fixed allocation size block, and chain
these blocks together as needed to make up the complete storage for
the string.
Strings are the very data type where I think the end user has to see
a contiguous string. In C/C++, the (const char *) is the only common
denominator
between string classes, all of which of course based on divine
revelation
but incompatible except for c_str()/CStr()/...
Eric Norum has an R3.14 IOC with very limited RAM that uses a waveform
record to allow its flash eprom to be reprogrammed, but his memory
requirements are such that he can only fit one waveform buffer in
memory. If we require another copy of the data this IOC would
probably not be able to fit in memory.
I don't see a realistic way around the fact that support for arbitrary
types
will require more memory.
Both buffer memory and additional code.
Similar to V3, something like EPICS_CA_MAX_ARRAY_BYTES
will define the biggest data type that your IOC can handle.
Given the same IOC memory, it will be a smaller number for V4 than it's
now for V3.
If you want to handle huge image but don't have the memory for it,
you'll have to work around it by writing the image line by line
into a smaller line array.
-Kay
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