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astrogo / fitsio

fitsio is a pure-Go package to read and write `FITS` files
BSD 3-Clause "New" or "Revised" License
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Data is lost when writing/reading table from map #59

Open dirodriguezm opened 4 months ago

dirodriguezm commented 4 months ago

Hi, I found that when writing and reading binary tables from a map, the recovered data is always zero value. For example strings are empty "" and numeric values are 0.

This can be easily replicated with the TestTableMapsRW in table_test.go. Even though the test passes, the values that are scanned to the map do not match with the original data.

I'm still a beginner at Go, but I think that calling reflect.Value.Interface returns the default value of the interface, so that's why it reads numeric values as 0 and strings as empty strings.

dirodriguezm commented 4 months ago

On further investigation I found that the problem is not when reading, but when writing. The writeMap function is writing 0 and also setting the original data as 0. What should be the correct behavior with this function ?

https://github.com/astrogo/fitsio/blob/f7769148dd4e12bc994ff06944e90f27a13d507c/table.go#L395-L423

On line 415 val is set as a reflect.New value which is 0 for numeric types. Then on line 420 the original data map is modified with this new 0 value which I don't understand.