str(3) Str 0.9.6 str(3)
String Library String Library
13-Sep-2001
NAME
Str - String Library
VERSION
Str 0.9.6 (13-Sep-2001)
SYNOPSIS
str_len, str_copy, str_dup, str_concat, str_splice, str_compare,
str_span, str_locate, str_token, str_parse, str_format, str_hash,
str_base64.
DESCRIPTION
The Str library is a generic string library written in ANSI C which
provides functions for handling, matching, parsing, searching and
formatting of C strings. So it can be considered as a superset of
POSIX string(3), but its main intention is to provide a more
convinient and compact API plus a more generalized functionality.
FUNCTIONS
The following functions are provided by the Str API:
str_size_t str_len(const char *s);
This function determines the length of string s, i.e., the number
of characters starting at s that precede the terminating "NUL"
character. It returns "NULL" if s is "NULL".
char *str_copy(char *s, const char *t, size_t n);
This copies the characters in string t into the string s, but
never more than n characters (if n is greater than "0"). The two
involved strings can overlap and the characters in s are always
"NUL"-terminated. The string s has to be large enough to hold all
characters to be copied. function returns "NULL" if s or t are
"NULL". Else it returns the pointer to the written
"NUL"-terminating character in s.
char *str_dup(const char *s, str_size_t n);
This returns a copy of the characters in string s, but never more
than n characters if n is greater than "0". It returns "NULL" if s
is "NULL". The returned string has to be deallocated later with
free(3).
char *str_concat(char *s, ...);
This functions concatenates the characters of all string arguments
into a new allocated string and returns this new string. If s is
"NULL" the function returns "NULL". Else it returns the pointer to
the written final "NUL"-terminating character in s. The returned
string later has to be deallicated with free(3).
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m);
char *str_splice(char *s, str_size_t off, str_size_t n, char *t, str_size_t
This splices the string t into string s, i.e., the n characters at
offset off in s are removed and at their location the string t is
inserted (or just the first m characters of t if m is greater than
"0"). It returns "NULL" if s or t are "NULL". Else the string s
is returned. The function supports also the situation where t is a
sub-string of s as long as the area s+off...s+off+n and t...t+m do
not overlap. The caller always has to make sure that enough room
exists in s.
int str_compare(const char *s, const char *t, str_size_t n, int mode);
This performs a lexicographical comparison of the two strings s
and t (but never compares more than n characters of them) and
returns one of three return values: a value lower than "0" if s is
lexicographically lower than t, a vlue of exactly "0" if s and t
are equal and a value greater than "0" if s is lexicographically
higher than t. Per default (mode is "0") the comparison is case-
sensitive, but if "STR_NOCASE" is used for mode the comparison is
done in a case-insensitive way.
char *str_span(const char *s, size_t n, const char *charset, int mode);
This functions spans a string s according to the characters
specified in charset. If mode is "0", this means that s is spanned
from left to right starting at s (and ending either when reaching
the terminating "NUL" character or already after n spanned
characters) as long as the characters of s are contained in
charset.
Alternatively one can use a mode of "STR_COMPLEMENT" to indicate
that s is spanned as long as the characters of s are not contained
in charset, i.e., charset then specifies the complement of the
spanning characters.
In both cases one can additionally "or" (with the C operator
``"|"'') "STR_RIGHT" into mode to indicate that the spanning is
done right to left starting at the terminating "NUL" character of
s (and ending either when reaching s or already after n spanned
characters).
char *str_locate(const char *s, str_size_t n, const char *t);
This functions searches for the (smaller) string t inside (larger)
string s. If n is not "0", the search is performed only inside the
first n characters of s.
*comment, int mode);
char *str_token(char **s, const char *delim, const char *quote, const char
This function considers the string s to consist of a sequence of
zero or more text tokens separated by spans of one or more
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characters from the separator string delim. However, text between
matched pairs of quotemarks (characters in quote) is treated as
plain text, never as delimiter (separator) text. Each call of this
function returns a pointer to the first character of the first
token of s. The token is "NUL"-terminated, i.e., the string s is
processed in a destructive way. If there are quotation marks or
escape sequences, the input string is rewritten with quoted
sections and escape sequences properly interpreted.
This function keeps track of its parsing position in the string
between separate calls by simply adjusting the callers s pointer,
so that subsequent calls with the same pointer variable s will
start processing from the position immediately after the last
returned token. In this way subsequent calls will work through
the string s until no tokens remain. When no token remains in s,
"NULL" is returned. The string of token separators (delim) and the
string of quote characters (quote) may be changed from call to
call.
If a character in the string s is not quoted or escaped, and is in
the comment set, then it is overwritten with a "NUL" character and
the rest of the string is ignored. The characters to be used as
quote characters are specified in the quote set, and must be used
in balanced pairs. If there is more than one flavor of quote
character, one kind of quote character may be used to quote
another kind. If an unbalanced quote is found, the function
silently act as if one had been placed at the end of the input
string. The delim and quote strings must be disjoint, i.e., they
have to share no characters.
The mode argument can be used to modify the processing of the
string (default for mode is "0"): "STR_STRIPQUOTES" forces quote
characters to be stripped from quoted tokens; "STR_BACKSLASHESC"
enables the interpretation (and expansion) of backslash escape
sequences (`\x') through ANSI-C rules; "STR_SKIPDELIMS" forces
that after the terminating "NUL" is written and the token
returned, further delimiters are skipped (this allows one to make
sure that the delimiters for one word don't become part of the
next word if one change delimiters between calls); and
"STR_TRIGRAPHS" enables the recognition and expansion of ANSI C
Trigraph sequences (as a side effect this enables
"STR_BACKSLASHESC", too).
int str_parse(const char *s, const char *pop, ...);
This parses the string s according to the parsing operation
specified by pop. If the parsing operation succeeds, "1" is
returned. If the parsing operation failed because the pattern pop
did not match, "0" is returned. If the parsing operation failed
because the underlying regular expression library failed, "-1" is
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returned.
The pop string usually has one of the following two syntax
variants: `m delim regex delim flags*' (for matching operations)
and `s delim regex delim subst delim flags*' (for substitution
operations). For more details about the syntax variants and
semantic of the pop argument see section GORY DETAILS, Parsing
Specification below. The syntax of the regex part in pop is mostly
equivalent to Perl 5's regular expression syntax. For the complete
and gory details see perlre(1). A brief summary you can find under
section GORY DETAILS, Perl Regular Expressions below.
int str_format(char *s, str_size_t n, const char *fmt, ...);
This formats a new string according to fmt and optionally
following arguments and writes it into the string s, but never
more than n characters at all. It returns the number of written
characters. If s is "NULL" it just calculates the number of
characters which would be written.
The function generates the output string under the control of the
fmt format string that specifies how subsequent arguments (or
arguments accessed via the variable-length argument facilities of
stdarg(3)) are converted for output.
The format string fmt is composed of zero or more directives:
ordinary characters (not %), which are copied unchanged to the
output stream; and conversion specifications, each of which
results in fetching zero or more subsequent arguments. Each
conversion specification is introduced by the character %. The
arguments must correspond properly (after type promotion) with the
conversion specifier. Which conversion specifications are
supported are described in detail under GORY DETAILS, Format
Specification below.
unsigned long str_hash(const char *s, str_size_t n, int mode);
This function calculates a hash value of string s (or of its first
n characters if n is equal to "0"). The following hashing
functions are supported and can be selected with mode:
STR_HASH_DJBX33 (Daniel J. Berstein, Times 33 Hash with Addition),
STR_HASH_BJDDJ (Bob Jenkins, Dr. Dobbs Journal), and
STR_HASH_MACRC32 (Mark Adler, Cyclic Redundancy Check with
32-Bit). This function is intended for fast use in hashing
algorithms and not for use as cryptographically strong message
digests.
int mode);
int str_base64(char *s, str_size_t n, unsigned char *ucp, str_size_t ucn,
This function Base64 encodes ucn bytes starting at ucp and writes
the resulting string into s (but never more than n characters are
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written). The mode for this operation has to be
"STR_BASE64_ENCODE". Additionally one can OR the value
"STR_BASE64_STRICT" to enable strict encoding where after every
72th output character a newline character is inserted. The
function returns the number of output characters written. If s is
"NULL" the function just calculates the number of required output
characters.
Alternatively, if mode is "STR_BASE64_DECODE" the string s (or the
first n characters only if n is not "0") is decoded and the output
bytes written at ucp. Again, if ucp is "NULL" only the number of
required output bytes are calculated.
GORY DETAILS
In this part of the documentation more complex topics are documented
in detail.
Perl Regular Expressions
The regular expressions used in Str are more or less Perl compatible
(they are provided by a stripped down and built-in version of the PCRE
library). So the syntax description in perlre(1) applies and don't has
to be repeated here again. For a deeper understanding and details you
should have a look at the book `Mastering Regular Expressions' (see
also the perlbook(1) manpage) by Jeffrey Friedl. For convinience
reasons we give you only a brief summary of Perl compatible regular
expressions:
The following metacharacters have their standard egrep(1) meanings:
\ Quote the next metacharacter
^ Match the beginning of the line
. Match any character (except newline)
$ Match the end of the line (or before newline at the end)
| Alternation
() Grouping
[] Character class
The following standard quantifiers are recognized:
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* Match 0 or more times (greedy)
*? Match 0 or more times (non greedy)
+ Match 1 or more times (greedy)
+? Match 1 or more times (non greedy)
? Match 1 or 0 times (greedy)
?? Match 1 or 0 times (non greedy)
{n} Match exactly n times (greedy)
{n}? Match exactly n times (non greedy)
{n,} Match at least n times (greedy)
{n,}? Match at least n times (non greedy)
{n,m} Match at least n but not more than m times (greedy)
{n,m}? Match at least n but not more than m times (non greedy)
The following backslash sequences are recognized:
\t Tab (HT, TAB)
\n Newline (LF, NL)
\r Return (CR)
\f Form feed (FF)
\a Alarm (bell) (BEL)
\e Escape (think troff) (ESC)
\033 Octal char
\x1B Hex char
\c[ Control char
\l Lowercase next char
\u Uppercase next char
\L Lowercase till \E
\U Uppercase till \E
\E End case modification
\Q Quote (disable) pattern metacharacters till \E
The following non zero-width assertions are recognized:
\w Match a "word" character (alphanumeric plus "_")
\W Match a non-word character
\s Match a whitespace character
\S Match a non-whitespace character
\d Match a digit character
\D Match a non-digit character
The following zero-width assertions are recognized:
\b Match a word boundary
\B Match a non-(word boundary)
\A Match only at beginning of string
\Z Match only at end of string, or before newline at the end
\z Match only at end of string
\G Match only where previous m//g left off (works only with /g)
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The following regular expression extensions are recognized:
(?#text) An embedded comment
(?:pattern) This is for clustering, not capturing (simple)
(?imsx-imsx:pattern) This is for clustering, not capturing (full)
(?=pattern) A zero-width positive lookahead assertion
(?!pattern) A zero-width negative lookahead assertion
(?<=pattern) A zero-width positive lookbehind assertion
(?<!pattern) A zero-width negative lookbehind assertion
(?>pattern) An "independent" subexpression
(?(cond)yes-re) Conditional expression (simple)
(?(cond)yes-re|no-re) Conditional expression (full)
(?imsx-imsx) One or more embedded pattern-match modifiers
Parsing Specification
The str_parse(const char *s, const char *pop, ...) function is a very
flexible but complex one. The argument s is the string on which the
parsing operation specified by argument pop is applied. The parsing
semantics are highly influenced by Perl's `=~' matching operator,
because one of the main goals of str_parse(3) is to allow one to
rewrite typical Perl matching constructs into C.
Now to the gory details. In general, the pop argument of str_parse(3)
has one of the following two syntax variants:
Matching: `m delim regex delim flags*':
This matches s against the Perl-style regular expression regex
under the control of zero or more flags which control the parsing
semantics. The stripped down pop syntax `regex' is equivalent to
`m/regex/'.
For each grouping pair of parenthesis in regex, the text in s
which was grouped by the parenthesis is extracted into new
strings. These per default are allocated as seperate strings and
returned to the caller through following `char **' arguments. The
caller is required to free(3) them later.
Substitution: `s delim regex delim subst delim flags*':
This matches s against the Perl-style regular expression regex
under the control of zero or more flags which control the parsing
semantics. As a result of the operation, a new string formed which
consists of s but with the part which matched regex replaced by
subst. The result string is returned to the caller through a `char
**' argument. The caller is required to free(3) this later.
For each grouping pair of parenthesis in regex, the text in s
which was grouped by the parenthesis is extracted into new strings
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and can be referenced for expansion via `$n' (n=1,..) in subst.
Additionally any str_format(3) style `%' constructs in subst are
expanded through additional caller supplied arguments.
The following flags are supported:
b If the bundle flag `b' is specified, the extracted strings are
bundled together into a single chunk of memory and its address is
returned to the caller with a additional `char **' argument which
has to preceed the regular string arguments. The caller then has
to free(3) only this chunk of memory in order to free all
extracted strings at once.
i If the case-insensitive flag `i' is specified, regex is matched in
case-insensitive way.
o If the once flag `o' is specified, this indicates to the Str
library that the whole pop string is constant and that its
internal pre-processing (it is compiled into a deterministic
finite automaton (DFA) internally) has to be done only once (the
Str library then caches the DFA which corresponds to the pop
argument).
x If the extended flag `x' is specified, the regex's legibility is
extended by permitting embedded whitespace and comments to allow
one to write down complex regular expressions more cleary and even
in a documented way.
m If the multiple lines flag `m' is specified, the string s is
treated as multiple lines. That is, this changes the regular
expression meta characters `^' and `$' from matching at only the
very start or end of the string s to the start or end of any line
anywhere within the string s.
s If the single line flag `s' is specified, the string s is treated
as single line. That is, this changes the regular expression meta
character `.' to match any character whatsoever, even a newline,
which it normally would not match.
CONVERSION SPECIFICATION
In the format string of str_format(3) each conversion specification is
introduced by the character %. After the %, the following appear in
sequence:
o An optional field, consisting of a decimal digit string followed
by a $, specifying the next argument to access. If this field is
not provided, the argument following the last argument accessed
will be used. Arguments are numbered starting at 1. If unaccessed
arguments in the format string are interspersed with ones that are
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accessed the results will be indeterminate.
o Zero or more of the following flags:
A # character specifying that the value should be converted to an
``alternate form''. For c, d, i, n, p, s, and u, conversions,
this option has no effect. For o conversions, the precision of
the number is increased to force the first character of the output
string to a zero (except if a zero value is printed with an
explicit precision of zero). For x and X conversions, a non-zero
result has the string 0x (or 0X for X conversions) prepended to
it. For e, E, f, g, and G, conversions, the result will always
contain a decimal point, even if no digits follow it (normally, a
decimal point appears in the results of those conversions only if
a digit follows). For g and G conversions, trailing zeros are not
removed from the result as they would otherwise be.
A zero `0' character specifying zero padding. For all conversions
except n, the converted value is padded on the left with zeros
rather than blanks. If a precision is given with a numeric
conversion (d, i, o, u, i, x, and X), the `0' flag is ignored.
A negative field width flag `-' indicates the converted value is
to be left adjusted on the field boundary. Except for n
conversions, the converted value is padded on the right with
blanks, rather than on the left with blanks or zeros. A `-'
overrides a `0' if both are given.
A space, specifying that a blank should be left before a positive
number produced by a signed conversion (d, e, E, f, g, G, or i).
A `+' character specifying that a sign always be placed before a
number produced by a signed conversion. A `+' overrides a space
if both are used.
o An optional decimal digit string specifying a minimum field width.
If the converted value has fewer characters than the field width,
it will be padded with spaces on the left (or right, if the left-
adjustment flag has been given) to fill out the field width.
o An optional precision, in the form of a period `.' followed by an
optional digit string. If the digit string is omitted, the
precision is taken as zero. This gives the minimum number of
digits to appear for d, i, o, u, x, and X conversions, the number
of digits to appear after the decimal-point for e, E, and f
conversions, the maximum number of significant digits for g and G
conversions, or the maximum number of characters to be printed
from a string for s conversions.
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o The optional character h, specifying that a following d, i, o, u,
x, or X conversion corresponds to a `"short int"' or `"unsigned
short int"' argument, or that a following n conversion corresponds
to a pointer to a `"short int" argument.
o The optional character l (ell) specifying that a following d, i,
o, u, x, or X conversion applies to a pointer to a `"long int"' or
`"unsigned long int"' argument, or that a following n conversion
corresponds to a pointer to a `"long int" argument.
o The optional character q, specifying that a following d, i, o, u,
x, or X conversion corresponds to a `"quad int"' or `"unsigned
quad int"' argument, or that a following n conversion corresponds
to a pointer to a `"quad int"' argument.
o The character L specifying that a following e, E, f, g, or G
conversion corresponds to a `"long double"' argument.
o A character that specifies the type of conversion to be applied.
A field width or precision, or both, may be indicated by an asterisk
`*' or an asterisk followed by one or more decimal digits and a `$'
instead of a digit string. In this case, an `"int"' argument supplies
the field width or precision. A negative field width is treated as a
left adjustment flag followed by a positive field width; a negative
precision is treated as though it were missing. If a single format
directive mixes positional (`nn$') and non-positional arguments, the
results are undefined.
The conversion specifiers and their meanings are:
diouxX
The `"int"' (or appropriate variant) argument is converted to
signed decimal (d and i), unsigned octal (o), unsigned decimal
(u), or unsigned hexadecimal (x and X) notation. The letters
abcdef are used for x conversions; the letters ABCDEF are used for
X conversions. The precision, if any, gives the minimum number of
digits that must appear; if the converted value requires fewer
digits, it is padded on the left with zeros.
DOU The `"long int" argument is converted to signed decimal, unsigned
octal, or unsigned decimal, as if the format had been ld, lo, or
lu respectively. These conversion characters are deprecated, and
will eventually disappear.
eE The `"double"' argument is rounded and converted in the style
`[-]d.ddde+-dd' where there is one digit before the decimal-point
character and the number of digits after it is equal to the
precision; if the precision is missing, it is taken as 6; if the
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precision is zero, no decimal-point character appears. An E
conversion uses the letter E (rather than e) to introduce the
exponent. The exponent always contains at least two digits; if
the value is zero, the exponent is 00.
f The `"double"' argument is rounded and converted to decimal
notation in the style `[-]ddd.ddd>' where the number of digits
after the decimal-point character is equal to the precision
specification. If the precision is missing, it is taken as 6; if
the precision is explicitly zero, no decimal-point character
appears. If a decimal point appears, at least one digit appears
before it.
g The `"double"' argument is converted in style f or e (or E for G
conversions). The precision specifies the number of significant
digits. If the precision is missing, 6 digits are given; if the
precision is zero, it is treated as 1. Style e is used if the
exponent from its conversion is less than -4 or greater than or
equal to the precision. Trailing zeros are removed from the
fractional part of the result; a decimal point appears only if it
is followed by at least one digit.
c The `"int"' argument is converted to an `"unsigned char", and the
resulting character is written.
s The `"char *"' argument is expected to be a pointer to an array of
character type (pointer to a string). Characters from the array
are written up to (but not including) a terminating "NUL"
character; if a precision is specified, no more than the number
specified are written. If a precision is given, no null character
need be present; if the precision is not specified, or is greater
than the size of the array, the array must contain a terminating
"NUL" character.
p The `"void *" pointer argument is printed in hexadecimal (as if by
`%#x' or `"%#lx").
n The number of characters written so far is stored into the integer
indicated by the `"int *"' (or variant) pointer argument. No
argument is converted.
% A `%' is written. No argument is converted. The complete
conversion specification is `%%.
In no case does a non-existent or small field width cause truncation
of a field; if the result of a conversion is wider than the field
width, the field is expanded to contain the conversion result.
EXAMPLES
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In the following a few snippets of selected use cases of Str are
presented:
Splice a String into Another
char *v1 = "foo bar quux";
char *v2 = "baz";
str_splice(v1, 3, 5, v2, 0):
/* now we have v1 = "foobazquux" */
....
Tokenize a String
char *var = " foo \t " bar 'baz'" q'uu'x #comment";
char *tok, *p;
p = var;
while ((tok = str_token(p, ":", "\"'", "#", 0)) != NULL) {
/* here we enter three times:
1. tok = "foo"
2. tok = " bar 'baz'"
3. tok = "quux" */
...
}
Match a String
char *var = "foo:bar";
if (str_parse(var, "^.+?:.+$/) > 0) {
/* var matched */
...
}
Match a String and Go Ahead with Details
char *var = "foo:bar";
char *cp, *v1, *v2;
if (str_parse(var, "m/^(.+?):(.+)$/b", &cp, &v1, &v2) > 0) {
...
/* now we have:
cp = "foo\0bar\0" and v1 and v2 pointing
into it, i.e., v1 = "foo", v2 = "bar" */
...
free(cp);
}
Substitute Text in a String
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char *var = "foo:bar";
char *subst = "quux";
char *new;
str_parse(var, "s/^(.+?):(.+)$/$1-%s-$2/", &new, subst);
...
/* now we have: var = "foo:bar", new = "foo:quux:bar" */
...
free(new);
Format a String
char *v0 = "abc..."; /* length not guessable */
char *v1 = "foo";
void *v2 = 0xDEAD;
int v3 = 42;
char *cp;
int n;
n = str_format(NULL, 0, "%s|%5s-%x-%04d", v0, v1, v2, v3);
cp = malloc(n);
str_format(cp, n, "%s-%x-%04d", v1, v2, v3);
/* now we have cp = "abc...| foo-DEAD-0042" */
...
free(cp);
SEE ALSO
string(3), printf(3), perlre(1).
HISTORY
The Str library was written in November and December 1999 by Ralf S.
Engelschall. As building blocks various existing code was used and
recycled: for the str_token(3) implementation an anchient strtok(3)
flavor from William Deich 1991 was cleaned up and adjusted. As the
background parsing engine for str_parse(3) a heavily stripped down
version of Philip Hazel's Perl Compatible Regular Expression (PCRE)
library (initially version 2.08 and now 3.5) was used. The
str_format(3) implementation was based on Panos Tsirigotis' sprintf(3)
code as adjusted by the Apache Software Foundation (ASF) 1998. The
formatting engine was stripped down and enhanced to support internal
extensions which were required by str_format(3) and str_parse(3).
AUTHOR
Ralf S. Engelschall
rse@engelschall.com
www.engelschall.com
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