void lxqstr_c ( ConstSpiceChar * string,
SpiceInt * last,
SpiceInt * nchar )
Lex (scan) a quoted string.
Variable I/O Description
-------- --- --------------------------------------------------
string I String to be scanned.
qchar I Quote delimiter character.
first I Character position at which to start scanning.
last O Character position of end of token.
nchar O Number of characters in token.
string is a character string that may contain a "string
token" starting at the character position
indicated by the input argument first (see below).
String tokens are sequences of characters that
represent literal strings. Syntactically, a string
token is a sequence of characters that begins and
ends with a designated "quote character". Within
the token, any occurrence of the quote character
is indicated by an adjacent pair of quote
characters: for example, if the quote character is
then the token representing one instance of this
Here the first quote indicates the beginning of the
token, the next two quotes together indicate a
single quote character that constitutes the
"contents" of the token, and the final quote
indicates the end of the token.
qchar is the quote character. This is always a single
character. The characters
" and '
are common choices, but any non-blank character is
accepted. Case *is* significant in qchar.
first is the character position at which the routine
is to start scanning a quoted string token. Note
that the character string[first] must equal
qchar if a string token is to be found; this
routine does *not* attempt to locate the first
quoted string following the position first.
last is the last character position such that the subtring
ranging from string[first] to string[last] is a
quoted string token, if such a substring exists.
Otherwise, the returned value of last is first-1.
nchar is the length of the string token found by this
routine, if such a token exists. This length
includes the starting and ending bracketing quotes.
If a string token is not found, the returned value
of nchar is zero.
1) If the input argument first is less than 1 or greater than
len(string)-1, the returned value of last is first-1, and the
returned value of nchar is zero.
2) It is not an error for a quoted string token to consist of
two consecutive quote characters with no intervening
characters. Calling routines that require special treatment
of null tokens must handle this case.
3) If the input argument qchar is blank, the returned value of
last is first-1, and the returned value of nchar is zero.
4) If the input string pointer is null, the error SPICE(NULLPOINTER)
will be signaled.
5) If the input string has length zero, last will be set to first-1
and nchar will be set to zero. This case is not considered an
Quote characters may be ANY non-blank character. For example, the
is a perfectly valid quote character. If we were using the
ampersand as the quote character, then the term "doubled quote"
in the following discussion would refer to the sequence
not the character
The string tokens identified by this routine are Fortran-style
quoted strings: they start and end with quote characters. In the
interior of any such token, any quote characters are represented
by doubled quote characters. These rules imply that the number of
quote characters in a quoted string token is always even. The end
of a quoted string token is located at the first even-numbered
quote character, counting from the initial quote character, that
is not the first member of a pair of quotes indicating an
embedded quote character.
To map the token to the string of characters it represents, use
the CSPICE subroutine parsqs_c (String parse, quoted). parsqs_c
removes the bracketing quotes from a quoted string token and
converts each doubled quote between the bracketing quotes to a
single quote. For example, the token
identified by this routine would be mapped by parsqs_c to a string
variable containing the single character
1) The table below illustrates the action of this routine.
STRING CONTENTS qchar first last nchar
The "SPICE" system " 4 10 7
The "SPICE" system " 0 -1 0
The "SPICE" system ' 4 3 0
The """SPICE"" system" " 4 12 9
The """SPICE"""" system " 4 14 11
The &&&SPICE system & 4 5 2
' ' ' 0 2 3
'' ' 0 1 2
N.J. Bachman (JPL)
-CSPICE Version 1.0.0, 19-AUG-2002 (NJB)
scan quoted string token
lex quoted string token
recognize quoted string token