| Re: Single Quotes, Double Quotes [message #11673] |
Mon, 18 May 1998 00:00  |
offenbrg
Messages: 31
Registered: August 1993
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Member |
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Charles Cavanaugh <cavanaug@nicole.eos.ucar.edu> writes:
> --------------F486C25E1BA64765FD765959
> Content-Type: text/plain; charset=us-ascii
> Content-Transfer-Encoding: 7bit
> Can anyone please explain to me why the line
> asciiutc = "1993-09-19T06:30:00.000000Z"
> fails compilation with the error message
> asciiutc = "1993-09-19T06:30:00.000000Z"
> ^
> % Syntax error.
> but the same line, using single quotes instead of double
> quotes, compiles.
The problem has to do with the way IDL creates octal (base-8) numbers.
To indicate that a number is octal, it is preceded by a double quote.
The problem arises when the leading character of your string is a numeral.
In your example, the "1 indicates an octal expression, which it processes
as a number (the 9s are confusing it a little); then it subtracts 09, a
decimal number, subtracts 19, and then comes to a T, which makes no sense
at all in an arithmetic expression, so it stops.
In short, the ' and the " are not interchangble WHEN the first character
of your string constant is a numeral.
Examples:
;
;Octal expression --- leading "
;
IDL> help,"123
<Expression> INT = 83
;
;String expression --- leading '
;
IDL> help,'123
<Expression> STRING = '123'
;
;Hexadecimal expression --- surrounded by '' with trailing x.
;
IDL> help,'123'x
<Expression> INT = 291
Hope all this helps!
Joel Offenberg
--
"...And I am unanimous in this" - Mrs. Slocumbe
------------------------------------------------------------ -----------------
| Joel D Offenberg | Joel.D.Offenbrg.1@gsfc.nasa.gov |
| Raytheon STX, NASA/GSFC/LASP & STScI | UIT & NGST (301) 286-5801 |
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