Once you've called this function on a header unit, subsequent fh_set*() calls will only affect the primary header unit. This has no effect on basic FITS, or if `hu' is already an extension.
`name' should be either "COMMENT" or "HISTORY" and `value' is the rest of the line (will be truncated at 72 characters.)
Set a logical or boolean FITS keyword. A non-zero `value' is saved as T(rue) and zero is saved as F(alse). Pass a NULL for `comment' to leave the old comment field (or no comment.)
Set an integer FITS keyword. Pass a NULL for `comment' to leave the old comment field (or no comment.)
Use this to set float (real) values. The value must be of type `double' and will be inserted in the FITS card as a number with a decimal point, and possibly an exponent (as determined by the %G format instruction to printf). `prec' is a precision value, which should reflect the number of significant figures in `value'.
When printing a year, with a century, prec should be at least 4 to ensure that the value does not get printed with an exponent by %G.
Pass a NULL for `comment' to leave the old comment field (or no comment.)
Set a string FITS keyword. If string is longer than 18 characters, the start of the comment field will be shifted, and a comment may get truncated.
Pass a NULL for `comment' to leave the old comment field (or no comment.)
Similar to fh_set_str(), but assumes that you have already sprintf'd the value into a buffer. Use this to get precise control over the formatting of the value field.
Merge source_hu into target_hu and sort according to the `idx' numbers that were in both lists. source_hu is not modified.