436 lines
17 KiB
C
436 lines
17 KiB
C
/*************************************************
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* PCRE2 DEMONSTRATION PROGRAM *
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*************************************************/
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/* This is a demonstration program to illustrate a straightforward way of
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using the PCRE2 regular expression library from a C program. See the
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pcre2sample documentation for a short discussion ("man pcre2sample" if you have
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the PCRE2 man pages installed). PCRE2 is a revised API for the library, and is
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incompatible with the original PCRE API.
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There are actually three libraries, each supporting a different code unit
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width. This demonstration program uses the 8-bit library. The default is to
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process each code unit as a separate character, but if the pattern begins with
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"(*UTF)", both it and the subject are treated as UTF-8 strings, where
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characters may occupy multiple code units.
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In Unix-like environments, if PCRE2 is installed in your standard system
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libraries, you should be able to compile this program using this command:
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cc -Wall pcre2demo.c -lpcre2-8 -o pcre2demo
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If PCRE2 is not installed in a standard place, it is likely to be installed
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with support for the pkg-config mechanism. If you have pkg-config, you can
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compile this program using this command:
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cc -Wall pcre2demo.c `pkg-config --cflags --libs libpcre2-8` -o pcre2demo
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If you do not have pkg-config, you may have to use something like this:
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cc -Wall pcre2demo.c -I/usr/local/include -L/usr/local/lib \
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-R/usr/local/lib -lpcre2-8 -o pcre2demo
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Replace "/usr/local/include" and "/usr/local/lib" with wherever the include and
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library files for PCRE2 are installed on your system. Only some operating
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systems (Solaris is one) use the -R option.
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Building under Windows:
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If you want to statically link this program against a non-dll .a file, you must
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define PCRE2_STATIC before including pcre2.h, so in this environment, uncomment
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the following line. */
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/* #define PCRE2_STATIC */
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/* The PCRE2_CODE_UNIT_WIDTH macro must be defined before including pcre2.h.
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For a program that uses only one code unit width, setting it to 8, 16, or 32
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makes it possible to use generic function names such as pcre2_compile(). Note
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that just changing 8 to 16 (for example) is not sufficient to convert this
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program to process 16-bit characters. Even in a fully 16-bit environment, where
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string-handling functions such as strcmp() and printf() work with 16-bit
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characters, the code for handling the table of named substrings will still need
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to be modified. */
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#define PCRE2_CODE_UNIT_WIDTH 8
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#include <stdio.h>
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#include <string.h>
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#include <pcre2.h>
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/**************************************************************************
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* Here is the program. The API includes the concept of "contexts" for *
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* setting up unusual interface requirements for compiling and matching, *
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* such as custom memory managers and non-standard newline definitions. *
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* This program does not do any of this, so it makes no use of contexts, *
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* always passing NULL where a context could be given. *
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**************************************************************************/
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int main(int argc, char **argv)
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{
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pcre2_code *re;
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PCRE2_SPTR pattern; /* PCRE2_SPTR is a pointer to unsigned code units of */
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PCRE2_SPTR subject; /* the appropriate width (in this case, 8 bits). */
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PCRE2_SPTR name_table;
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int crlf_is_newline;
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int errornumber;
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int find_all;
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int i;
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int rc;
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int utf8;
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uint32_t option_bits;
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uint32_t namecount;
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uint32_t name_entry_size;
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uint32_t newline;
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PCRE2_SIZE erroroffset;
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PCRE2_SIZE *ovector;
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size_t subject_length;
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pcre2_match_data *match_data;
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/**************************************************************************
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* First, sort out the command line. There is only one possible option at *
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* the moment, "-g" to request repeated matching to find all occurrences, *
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* like Perl's /g option. We set the variable find_all to a non-zero value *
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* if the -g option is present. *
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**************************************************************************/
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find_all = 0;
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for (i = 1; i < argc; i++)
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{
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if (strcmp(argv[i], "-g") == 0) find_all = 1;
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else if (argv[i][0] == '-')
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{
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printf("Unrecognised option %s\n", argv[i]);
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return 1;
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}
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else break;
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}
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/* After the options, we require exactly two arguments, which are the pattern,
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and the subject string. */
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if (argc - i != 2)
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{
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printf("Exactly two arguments required: a regex and a subject string\n");
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return 1;
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}
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/* As pattern and subject are char arguments, they can be straightforwardly
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cast to PCRE2_SPTR as we are working in 8-bit code units. */
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pattern = (PCRE2_SPTR)argv[i];
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subject = (PCRE2_SPTR)argv[i+1];
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subject_length = strlen((char *)subject);
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/*************************************************************************
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* Now we are going to compile the regular expression pattern, and handle *
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* any errors that are detected. *
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*************************************************************************/
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re = pcre2_compile(
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pattern, /* the pattern */
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PCRE2_ZERO_TERMINATED, /* indicates pattern is zero-terminated */
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0, /* default options */
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&errornumber, /* for error number */
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&erroroffset, /* for error offset */
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NULL); /* use default compile context */
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/* Compilation failed: print the error message and exit. */
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if (re == NULL)
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{
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PCRE2_UCHAR buffer[256];
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pcre2_get_error_message(errornumber, buffer, sizeof(buffer));
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printf("PCRE2 compilation failed at offset %d: %s\n", (int)erroroffset,
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buffer);
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return 1;
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}
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/*************************************************************************
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* If the compilation succeeded, we call PCRE again, in order to do a *
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* pattern match against the subject string. This does just ONE match. If *
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* further matching is needed, it will be done below. Before running the *
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* match we must set up a match_data block for holding the result. *
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*************************************************************************/
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/* Using this function ensures that the block is exactly the right size for
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the number of capturing parentheses in the pattern. */
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match_data = pcre2_match_data_create_from_pattern(re, NULL);
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rc = pcre2_match(
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re, /* the compiled pattern */
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subject, /* the subject string */
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subject_length, /* the length of the subject */
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0, /* start at offset 0 in the subject */
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0, /* default options */
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match_data, /* block for storing the result */
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NULL); /* use default match context */
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/* Matching failed: handle error cases */
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if (rc < 0)
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{
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switch(rc)
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{
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case PCRE2_ERROR_NOMATCH: printf("No match\n"); break;
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/*
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Handle other special cases if you like
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*/
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default: printf("Matching error %d\n", rc); break;
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}
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pcre2_match_data_free(match_data); /* Release memory used for the match */
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pcre2_code_free(re); /* data and the compiled pattern. */
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return 1;
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}
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/* Match succeded. Get a pointer to the output vector, where string offsets are
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stored. */
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ovector = pcre2_get_ovector_pointer(match_data);
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printf("Match succeeded at offset %d\n", (int)ovector[0]);
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/*************************************************************************
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* We have found the first match within the subject string. If the output *
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* vector wasn't big enough, say so. Then output any substrings that were *
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* captured. *
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*************************************************************************/
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/* The output vector wasn't big enough. This should not happen, because we used
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pcre2_match_data_create_from_pattern() above. */
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if (rc == 0)
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printf("ovector was not big enough for all the captured substrings\n");
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/* Show substrings stored in the output vector by number. Obviously, in a real
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application you might want to do things other than print them. */
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for (i = 0; i < rc; i++)
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{
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PCRE2_SPTR substring_start = subject + ovector[2*i];
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size_t substring_length = ovector[2*i+1] - ovector[2*i];
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printf("%2d: %.*s\n", i, (int)substring_length, (char *)substring_start);
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}
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/**************************************************************************
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* That concludes the basic part of this demonstration program. We have *
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* compiled a pattern, and performed a single match. The code that follows *
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* shows first how to access named substrings, and then how to code for *
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* repeated matches on the same subject. *
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**************************************************************************/
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/* See if there are any named substrings, and if so, show them by name. First
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we have to extract the count of named parentheses from the pattern. */
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(void)pcre2_pattern_info(
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re, /* the compiled pattern */
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PCRE2_INFO_NAMECOUNT, /* get the number of named substrings */
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&namecount); /* where to put the answer */
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if (namecount == 0) printf("No named substrings\n"); else
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{
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PCRE2_SPTR tabptr;
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printf("Named substrings\n");
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/* Before we can access the substrings, we must extract the table for
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translating names to numbers, and the size of each entry in the table. */
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(void)pcre2_pattern_info(
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re, /* the compiled pattern */
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PCRE2_INFO_NAMETABLE, /* address of the table */
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&name_table); /* where to put the answer */
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(void)pcre2_pattern_info(
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re, /* the compiled pattern */
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PCRE2_INFO_NAMEENTRYSIZE, /* size of each entry in the table */
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&name_entry_size); /* where to put the answer */
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/* Now we can scan the table and, for each entry, print the number, the name,
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and the substring itself. In the 8-bit library the number is held in two
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bytes, most significant first. */
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tabptr = name_table;
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for (i = 0; i < namecount; i++)
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{
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int n = (tabptr[0] << 8) | tabptr[1];
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printf("(%d) %*s: %.*s\n", n, name_entry_size - 3, tabptr + 2,
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(int)(ovector[2*n+1] - ovector[2*n]), subject + ovector[2*n]);
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tabptr += name_entry_size;
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}
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}
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/*************************************************************************
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* If the "-g" option was given on the command line, we want to continue *
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* to search for additional matches in the subject string, in a similar *
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* way to the /g option in Perl. This turns out to be trickier than you *
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* might think because of the possibility of matching an empty string. *
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* What happens is as follows: *
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* *
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* If the previous match was NOT for an empty string, we can just start *
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* the next match at the end of the previous one. *
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* *
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* If the previous match WAS for an empty string, we can't do that, as it *
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* would lead to an infinite loop. Instead, a call of pcre2_match() is *
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* made with the PCRE2_NOTEMPTY_ATSTART and PCRE2_ANCHORED flags set. The *
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* first of these tells PCRE2 that an empty string at the start of the *
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* subject is not a valid match; other possibilities must be tried. The *
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* second flag restricts PCRE2 to one match attempt at the initial string *
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* position. If this match succeeds, an alternative to the empty string *
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* match has been found, and we can print it and proceed round the loop, *
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* advancing by the length of whatever was found. If this match does not *
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* succeed, we still stay in the loop, advancing by just one character. *
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* In UTF-8 mode, which can be set by (*UTF) in the pattern, this may be *
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* more than one byte. *
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* *
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* However, there is a complication concerned with newlines. When the *
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* newline convention is such that CRLF is a valid newline, we must *
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* advance by two characters rather than one. The newline convention can *
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* be set in the regex by (*CR), etc.; if not, we must find the default. *
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*************************************************************************/
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if (!find_all) /* Check for -g */
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{
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pcre2_match_data_free(match_data); /* Release the memory that was used */
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pcre2_code_free(re); /* for the match data and the pattern. */
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return 0; /* Exit the program. */
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}
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/* Before running the loop, check for UTF-8 and whether CRLF is a valid newline
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sequence. First, find the options with which the regex was compiled and extract
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the UTF state. */
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(void)pcre2_pattern_info(re, PCRE2_INFO_ALLOPTIONS, &option_bits);
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utf8 = (option_bits & PCRE2_UTF) != 0;
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/* Now find the newline convention and see whether CRLF is a valid newline
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sequence. */
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(void)pcre2_pattern_info(re, PCRE2_INFO_NEWLINE, &newline);
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crlf_is_newline = newline == PCRE2_NEWLINE_ANY ||
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newline == PCRE2_NEWLINE_CRLF ||
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newline == PCRE2_NEWLINE_ANYCRLF;
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/* Loop for second and subsequent matches */
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for (;;)
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{
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uint32_t options = 0; /* Normally no options */
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PCRE2_SIZE start_offset = ovector[1]; /* Start at end of previous match */
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/* If the previous match was for an empty string, we are finished if we are
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at the end of the subject. Otherwise, arrange to run another match at the
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same point to see if a non-empty match can be found. */
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if (ovector[0] == ovector[1])
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{
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if (ovector[0] == subject_length) break;
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options = PCRE2_NOTEMPTY_ATSTART | PCRE2_ANCHORED;
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}
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/* Run the next matching operation */
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rc = pcre2_match(
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re, /* the compiled pattern */
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subject, /* the subject string */
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subject_length, /* the length of the subject */
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start_offset, /* starting offset in the subject */
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options, /* options */
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match_data, /* block for storing the result */
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NULL); /* use default match context */
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/* This time, a result of NOMATCH isn't an error. If the value in "options"
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is zero, it just means we have found all possible matches, so the loop ends.
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Otherwise, it means we have failed to find a non-empty-string match at a
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point where there was a previous empty-string match. In this case, we do what
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Perl does: advance the matching position by one character, and continue. We
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do this by setting the "end of previous match" offset, because that is picked
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up at the top of the loop as the point at which to start again.
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There are two complications: (a) When CRLF is a valid newline sequence, and
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the current position is just before it, advance by an extra byte. (b)
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Otherwise we must ensure that we skip an entire UTF character if we are in
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UTF mode. */
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if (rc == PCRE2_ERROR_NOMATCH)
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{
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if (options == 0) break; /* All matches found */
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ovector[1] = start_offset + 1; /* Advance one code unit */
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if (crlf_is_newline && /* If CRLF is a newline & */
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start_offset < subject_length - 1 && /* we are at CRLF, */
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subject[start_offset] == '\r' &&
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subject[start_offset + 1] == '\n')
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ovector[1] += 1; /* Advance by one more. */
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else if (utf8) /* Otherwise, ensure we */
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{ /* advance a whole UTF-8 */
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while (ovector[1] < subject_length) /* character. */
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{
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if ((subject[ovector[1]] & 0xc0) != 0x80) break;
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ovector[1] += 1;
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}
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}
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continue; /* Go round the loop again */
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}
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/* Other matching errors are not recoverable. */
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if (rc < 0)
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{
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printf("Matching error %d\n", rc);
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pcre2_match_data_free(match_data);
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pcre2_code_free(re);
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return 1;
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}
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/* Match succeded */
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printf("\nMatch succeeded again at offset %d\n", (int)ovector[0]);
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/* The match succeeded, but the output vector wasn't big enough. This
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should not happen. */
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if (rc == 0)
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printf("ovector was not big enough for all the captured substrings\n");
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/* As before, show substrings stored in the output vector by number, and then
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also any named substrings. */
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for (i = 0; i < rc; i++)
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{
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PCRE2_SPTR substring_start = subject + ovector[2*i];
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size_t substring_length = ovector[2*i+1] - ovector[2*i];
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printf("%2d: %.*s\n", i, (int)substring_length, (char *)substring_start);
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}
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if (namecount == 0) printf("No named substrings\n"); else
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{
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PCRE2_SPTR tabptr = name_table;
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printf("Named substrings\n");
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for (i = 0; i < namecount; i++)
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{
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int n = (tabptr[0] << 8) | tabptr[1];
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printf("(%d) %*s: %.*s\n", n, name_entry_size - 3, tabptr + 2,
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(int)(ovector[2*n+1] - ovector[2*n]), subject + ovector[2*n]);
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tabptr += name_entry_size;
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}
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}
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} /* End of loop to find second and subsequent matches */
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printf("\n");
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pcre2_match_data_free(match_data);
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pcre2_code_free(re);
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return 0;
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}
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/* End of pcre2demo.c */
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