| Writing a structure containing empty strings [message #49607] |
Mon, 07 August 2006 08:12 |
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Messages: 47
Registered: August 2003
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This message and the next one address long-standing problems I've had
with IDL software to handle the FITS data format used in astronomy.
When writing an IDL structure, str, to FITS format, the following
simple code *almost* works.
openw,lun, 'output.dat',/get_lun
writeu,lun, str
free_lun, lun
The only problem occurs if one of the structure tags contains an empty
string. What I want is for IDL to write a zeroed byte (0b), but IDL
simply ignores the tag and doesn't write anything. Note that IDL
does understand 0b as the byte representation of an empty string:
IDL> print,strlen(string(0b))
0
IDL> print,byte('')
0
but it simply skip over an empty string when performing I/O. So my
first thought is to convert the string tags to bytes, but this has two
problems: (1) one can't directly change the data type of a structure
tag and (2) converting a string array to byte forces everything to a
fixed length. So right now, I loop over every element and every tag
of the structure and write it to disk:, if it is a string tag I test
for the presence of an empty string, and then further loop over the
string array to convert every element to a byte array before writing to
disk. So simple code that *almost* works, requires a major revision
to completely work. Or am I missing a simpler solution?
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