C API: StringSearch. More...
Go to the source code of this file.
#define USEARCH_DONE -1 DONE is returned by previous() and next() after all valid matches have been returned, and by first() and last() if there are no matches at all. More...usearch_first, usearch_next, usearch_previous, or usearch_last. More...
position at which the string text matches the search pattern. More...
position at which the string text matches the search pattern. More...
C API: StringSearch.
C APIs for an engine that provides language-sensitive text searching based on the comparison rules defined in a UCollator data struct, see ucol.h. This ensures that language eccentricity can be handled, e.g. for the German collator, characters ß and SS will be matched if case is chosen to be ignored. See the "ICU Collation Design Document" for more information.
As of ICU4C 4.0 / ICU4J 53, the implementation uses a linear search. In previous versions, a modified form of the Boyer-Moore searching algorithm was used. For more information on the modified Boyer-Moore algorithm see "Efficient Text Searching in Java", published in Java Report in February, 1999.
There are 2 match options for selection:
Let S' be the sub-string of a text string S between the offsets start and end <start, end>.
A pattern string P matches a text string S at the offsets <start, end> if
option 1. Some canonical equivalent of P matches some canonical equivalent
of S'
option 2. P matches S' and if P starts or ends with a combining mark,
there exists no non-ignorable combining mark before or after S'
in S respectively.
Option 2. will be the default.
This search has APIs similar to that of other text iteration mechanisms such as the break iterators in ubrk.h. Using these APIs, it is easy to scan through text looking for all occurrences of a given pattern. This search iterator allows changing of direction by calling a reset followed by a next or previous. Though a direction change can occur without calling reset first,
this operation comes with some speed penalty. Generally, match results in the forward direction will match the result matches in the backwards direction in the reverse order
usearch.h provides APIs to specify the starting position within the text string to be searched, e.g. usearch_setOffset, usearch_preceding and usearch_following. Since the starting position will be set as it is specified, please take note that there are some dangerous positions which the search may render incorrect results:
A breakiterator can be used if only matches at logical breaks are desired. Using a breakiterator will only give you results that exactly matches the boundaries given by the breakiterator. For instance the pattern "e" will not be found in the string "\u00e9" if a character break iterator is used.
Options are provided to handle overlapping matches. E.g. In English, overlapping matches produces the result 0 and 2 for the pattern "abab" in the text "ababab", where else mutually exclusive matches only produce the result of 0.
Options are also provided to implement "asymmetric search" as described in UTS #10 Unicode Collation Algorithm, specifically the USearchAttribute USEARCH_ELEMENT_COMPARISON and its values.
Though collator attributes will be taken into consideration while performing matches, there are no APIs here for setting and getting the attributes. These attributes can be set by getting the collator from usearch_getCollator and using the APIs in ucol.h. Lastly to update String Search to the new collator attributes, usearch_reset() has to be called.
Restriction:
Currently there are no composite characters that consists of a character with combining class > 0 before a character with combining class == 0. However, if such a character exists in the future, the search mechanism does not guarantee the results for option 1.
Example of use:
char *tgtstr = "The quick brown fox jumped over the lazy fox";
char *patstr = "fox";
UChar target[64];
UChar pattern[16];
UErrorCode status = U_ZERO_ERROR;
u_uastrcpy(target, tgtstr);
u_uastrcpy(pattern, patstr);
UStringSearch *search = usearch_open(pattern, -1, target, -1, "en_US",
NULL, &status);
if (U_SUCCESS(status)) {
for (int pos = usearch_first(search, &status);
pos != USEARCH_DONE;
pos = usearch_next(search, &status))
{
printf("Found match at %d pos, length is %d\n", pos,
usearch_getMatchedLength(search));
}
}
usearch_close(search);
Definition in file usearch.h.
◆ USEARCH_DONEDONE is returned by previous() and next() after all valid matches have been returned, and by first() and last() if there are no matches at all.
Definition at line 151 of file usearch.h.
◆ UStringSearchData structure for searching.
Definition at line 1 of file usearch.h.
◆ USearchAttributeOption for overlapping matches.
Option for canonical matches; option 1 in header documentation.
The default value will be USEARCH_OFF. Note: Setting this option to USEARCH_ON currently has no effect on search behavior, and this option is deprecated. Instead, to control canonical match behavior, you must set UCOL_NORMALIZATION_MODE appropriately (to UCOL_OFF or UCOL_ON) in the UCollator used by the UStringSearch object.
Option to control how collation elements are compared.
The default value will be USEARCH_STANDARD_ELEMENT_COMPARISON.
One more than the highest normal USearchAttribute value.
Definition at line 167 of file usearch.h.
◆ USearchAttributeValueDefault value for any USearchAttribute.
Value for USEARCH_OVERLAP and USEARCH_CANONICAL_MATCH.
Value for USEARCH_OVERLAP and USEARCH_CANONICAL_MATCH.
Value (default) for USEARCH_ELEMENT_COMPARISON; standard collation element comparison at the specified collator strength.
Value for USEARCH_ELEMENT_COMPARISON; collation element comparison is modified to effectively provide behavior between the specified strength and strength - 1.
Collation elements in the pattern that have the base weight for the specified strength are treated as "wildcards" that match an element with any other weight at that collation level in the searched text. For example, with a secondary-strength English collator, a plain 'e' in the pattern will match a plain e or an e with any diacritic in the searched text, but an e with diacritic in the pattern will only match an e with the same diacritic in the searched text.
This supports "asymmetric search" as described in UTS #10 Unicode Collation Algorithm.
Value for USEARCH_ELEMENT_COMPARISON.
collation element comparison is modified to effectively provide behavior between the specified strength and strength - 1. Collation elements in either the pattern or the searched text that have the base weight for the specified strength are treated as "wildcards" that match an element with any other weight at that collation level. For example, with a secondary-strength English collator, a plain 'e' in the pattern will match a plain e or an e with any diacritic in the searched text, but an e with diacritic in the pattern will only match an e with the same diacritic or a plain e in the searched text.
This option is similar to "asymmetric search" as described in UTS #10 Unicode Collation Algorithm, but also allows unmarked characters in the searched text to match marked or unmarked versions of that character in the pattern.
One more than the highest normal USearchAttributeValue value.
Definition at line 209 of file usearch.h.
◆ usearch_close()Destroys and cleans up the String Search iterator data struct.
If a collator was created in usearch_open, then it will be destroyed here.
Returns the first index at which the string text matches the search pattern.
The iterator is adjusted so that its current index (as returned by usearch_getOffset) is the match position if one was found. If a match is not found, USEARCH_DONE will be returned and the iterator will be adjusted to the index USEARCH_DONE.
USEARCH_DONE if there are no matches.
Returns the first index equal or greater than position at which the string text matches the search pattern.
The iterator is adjusted so that its current index (as returned by usearch_getOffset) is the match position if one was found. If a match is not found, USEARCH_DONE will be returned and the iterator will be adjusted to the index USEARCH_DONE
Search positions that may render incorrect results are highlighted in the header comments. If position is less than or greater than the text range for searching, an U_INDEX_OUTOFBOUNDS_ERROR will be returned
pos, or USEARCH_DONE if there are no matches.
Gets the text searching attributes.
Returns the BreakIterator that is used to restrict the points at which matches are detected.
This will be the same object that was passed to the constructor or to usearch_setBreakIterator. Note that NULL is a legal value; it means that break detection should not be attempted.
Gets the collator used for the language rules.
Deleting the returned UCollator before calling usearch_close would cause the string search to fail. usearch_close will delete the collator if this search owns it.
Returns the length of text in the string which matches the search pattern.
This call returns a valid result only after a successful call to usearch_first, usearch_next, usearch_previous, or usearch_last. Just after construction, or after a searching method returns USEARCH_DONE, this method will return 0.
Returns the index to the match in the text string that was searched.
This call returns a valid result only after a successful call to usearch_first, usearch_next, usearch_previous, or usearch_last. Just after construction, or after a searching method returns USEARCH_DONE, this method will return USEARCH_DONE.
Use usearch_getMatchedLength to get the matched string length.
Returns the text that was matched by the most recent call to usearch_first, usearch_next, usearch_previous, or usearch_last.
If the iterator is not pointing at a valid match (e.g. just after construction or after USEARCH_DONE has been returned, returns an empty string. If result is not large enough to store the matched text, result will be filled with the partial text and an U_BUFFER_OVERFLOW_ERROR will be returned in status. result will be null-terminated whenever possible. If the buffer fits the matched text exactly, a null-termination is not possible, then a U_STRING_NOT_TERMINATED_ERROR set in status. Pre-flighting can be either done with length = 0 or the API usearch_getMatchedLength.
Return the current index in the string text being searched.
If the iteration has gone past the end of the text (or past the beginning for a backwards search), USEARCH_DONE is returned.
Gets the search pattern.
Return the string text to be searched.
Returns the last index in the target text at which it matches the search pattern.
The iterator is adjusted so that its current index (as returned by usearch_getOffset) is the match position if one was found. If a match is not found, USEARCH_DONE will be returned and the iterator will be adjusted to the index USEARCH_DONE.
USEARCH_DONE if there are no matches.
Returns the index of the next point at which the string text matches the search pattern, starting from the current position.
The iterator is adjusted so that its current index (as returned by usearch_getOffset) is the match position if one was found. If a match is not found, USEARCH_DONE will be returned and the iterator will be adjusted to the index USEARCH_DONE
USEARCH_DONE if there are no more matches.
Creates a String Search iterator data struct using the argument locale language rule set.
A collator will be created in the process, which will be owned by this String Search and will be deleted in usearch_close.
The UStringSearch retains a pointer to both the pattern and text strings. The caller must not modify or delete them while using the UStringSearch.
BreakIterator, the match will be rejected and another will be searched for. If this parameter is NULL, no break detection is attempted. status for errors if it occurs. If pattern or text is NULL, or if patternlength or textlength is 0 then an U_ILLEGAL_ARGUMENT_ERROR is returned.
Creates a String Search iterator data struct using the argument collator language rule set.
Note, user retains the ownership of this collator, thus the responsibility of deletion lies with the user.
NOTE: String Search cannot be instantiated from a collator that has collate digits as numbers (CODAN) turned on (UCOL_NUMERIC_COLLATION).
The UStringSearch retains a pointer to both the pattern and text strings. The caller must not modify or delete them while using the UStringSearch.
BreakIterator, the match will be rejected and another will be searched for. If this parameter is NULL, no break detection is attempted. status for errors if it occurs. If collator, pattern or text is NULL, or if patternlength or textlength is 0 then an U_ILLEGAL_ARGUMENT_ERROR is returned.
Returns the first index less than position at which the string text matches the search pattern.
The iterator is adjusted so that its current index (as returned by usearch_getOffset) is the match position if one was found. If a match is not found, USEARCH_DONE will be returned and the iterator will be adjusted to the index USEARCH_DONE
Search positions that may render incorrect results are highlighted in the header comments. If position is less than or greater than the text range for searching, an U_INDEX_OUTOFBOUNDS_ERROR will be returned.
When USEARCH_OVERLAP option is off, the last index of the result match is always less than position. When USERARCH_OVERLAP is on, the result match may span across position.
pos, or USEARCH_DONE if there are no matches.
Returns the index of the previous point at which the string text matches the search pattern, starting at the current position.
The iterator is adjusted so that its current index (as returned by usearch_getOffset) is the match position if one was found. If a match is not found, USEARCH_DONE will be returned and the iterator will be adjusted to the index USEARCH_DONE
USEARCH_DONE if there are no more matches.
Reset the iteration.
Search will begin at the start of the text string if a forward iteration is initiated before a backwards iteration. Otherwise if a backwards iteration is initiated before a forwards iteration, the search will begin at the end of the text string.
Simple forward search for the pattern, starting at a specified index, and using a default set search options.
This is an experimental function, and is not an official part of the ICU API.
The collator options, such as UCOL_STRENGTH and UCOL_NORMALIZTION, are honored.
The UStringSearch options USEARCH_CANONICAL_MATCH, USEARCH_OVERLAP and any Break Iterator are ignored.
Matches obey the following constraints:
Characters at the start or end positions of a match that are ignorable for collation are not included as part of the match, unless they are part of a combining sequence, as described below. A match will not include a partial combining sequence. Combining character sequences are considered to be inseparable units, and either match the pattern completely, or are considered to not match at all. Thus, for example, an A followed a combining accent mark will not be found when searching for a plain (unaccented) A. (unless the collation strength has been set to ignore all accents). When beginning a search, the initial starting position, startIdx, is assumed to be an acceptable match boundary with respect to combining characters. A combining sequence that spans across the starting point will not suppress a match beginning at startIdx. Characters that expand to multiple collation elements (German sharp-S becoming 'ss', or the composed forms of accented characters, for example) also must match completely. Searching for a single 's' in a string containing only a sharp-s will find no match.
Simple backwards search for the pattern, starting at a specified index, and using using a default set search options.
This is an experimental function, and is not an official part of the ICU API.
The collator options, such as UCOL_STRENGTH and UCOL_NORMALIZTION, are honored.
The UStringSearch options USEARCH_CANONICAL_MATCH, USEARCH_OVERLAP and any Break Iterator are ignored.
Matches obey the following constraints:
Characters at the start or end positions of a match that are ignorable for collation are not included as part of the match, unless they are part of a combining sequence, as described below. A match will not include a partial combining sequence. Combining character sequences are considered to be inseparable units, and either match the pattern completely, or are considered to not match at all. Thus, for example, an A followed a combining accent mark will not be found when searching for a plain (unaccented) A. (unless the collation strength has been set to ignore all accents). When beginning a search, the initial starting position, startIdx, is assumed to be an acceptable match boundary with respect to combining characters. A combining sequence that spans across the starting point will not suppress a match beginning at startIdx. Characters that expand to multiple collation elements (German sharp-S becoming 'ss', or the composed forms of accented characters, for example) also must match completely. Searching for a single 's' in a string containing only a sharp-s will find no match.
Sets the text searching attributes located in the enum USearchAttribute with values from the enum USearchAttributeValue.
USEARCH_DEFAULT can be used for all attributes for resetting.
Set the BreakIterator that will be used to restrict the points at which matches are detected.
BreakIterator, the match will be rejected and another will be searched for. If this parameter is NULL, no break detection is attempted. status for errors if it occurs
Sets the collator used for the language rules.
User retains the ownership of this collator, thus the responsibility of deletion lies with the user. This method causes internal data such as the pattern collation elements and shift tables to be recalculated, but the iterator's position is unchanged.
Sets the current position in the text string which the next search will start from.
Clears previous states. This method takes the argument index and sets the position in the text string accordingly without checking if the index is pointing to a valid starting point to begin searching. Search positions that may render incorrect results are highlighted in the header comments
Sets the pattern used for matching.
Internal data like the pattern collation elements will be recalculated, but the iterator's position is unchanged.
The UStringSearch retains a pointer to the pattern string. The caller must not modify or delete the string while using the UStringSearch.
Set the string text to be searched.
Text iteration will hence begin at the start of the text string. This method is useful if you want to re-use an iterator to search for the same pattern within a different body of text.
The UStringSearch retains a pointer to the text string. The caller must not modify or delete the string while using the UStringSearch.
RetroSearch is an open source project built by @garambo | Open a GitHub Issue
Search and Browse the WWW like it's 1997 | Search results from DuckDuckGo
HTML:
3.2
| Encoding:
UTF-8
| Version:
0.7.4