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Match and Capture - Regular Expressions
Character Strings example from a Well House Consultants training course
More on Character Strings [link]
Source code: reg2.c Module: C206
/* The C language comes with a regular expression engine as standard and
a header file in regex.h. In this example program, we ask the user to enter a regular expression and then match it against a series of further strings. There is a shorter example at reg.c ... this example (reg2.c) caputures the start and end point of each match and then prints out the string that matches that part of the incoming string- "capture parenthises" */ #include <stdio.h> #include <string.h> #include <stdlib.h> #include <regex.h> #define MAXMATCH 20 int main () { char reginald[81]; /* Regular Expresion */ char millie[81]; /* Strings to match against */ char tommy[81]; /* String to hold matched elememts */ regex_t emma; regmatch_t matches[MAXMATCH]; /* Array of matches */ int status; int i; int numchars; /* Read in and compile a regular expression */ printf("Please give test expression: "); fgets(reginald,80,stdin); reginald[strlen(reginald)-1] = '\0'; /* Let's use extended regular expresssions */ status = regcomp(&emma,reginald,REG_EXTENDED); printf("Validity of regex (0 => OK): %d\n",status); /* Leave program if regex is faulty */ /* we could use regerror to decode the error ... */ if (status) return 1; while (1) { /* Loop until an empty line id given */ printf("Please give test string: "); fgets(millie,80,stdin); millie[strlen(millie)-1] = '\0'; if (strlen(millie) < 1) break; status = regexec(&emma,millie,MAXMATCH,matches,0); printf("Matched (0 => Yes): %d\n",status); if (status == 0) { for (i=0; i<MAXMATCH; i++) { if ((int)matches[i].rm_so < 0) break; numchars = (int)matches[i].rm_eo - (int)matches[i].rm_so; strncpy(tommy,millie+matches[i].rm_so,numchars); tommy[numchars] = '\0'; printf("From %d to %d (%s)\n",(int)matches[i].rm_so, (int)matches[i].rm_eo,tommy); } } } /* Free up memory held within the regex memory */ regfree(&emma); return 0; } /* Sample output: wizzard:c graham$ ./reg2 Please give test expression: [A-Z]{1,2}[0-9][0-9A-Z]? +[0-9][A-Z]{2} Validity of regex (0 => OK): 0 Please give test string: We are at SN12 7NY for this course Matched (0 => Yes): 0 From 10 to 18 (SN12 7NY) Please give test string: wizzard:c graham$ wizzard:c graham$ ./reg2 Please give test expression: ([A-Z]{1,2})[0-9][0-9A-Z]? +[0-9][A-Z]{2} Validity of regex (0 => OK): 0 Please give test string: We are in Birmingham Matched (0 => Yes): 1 Please give test string: We are at B12 7HJ Matched (0 => Yes): 0 From 10 to 17 (B12 7HJ) From 10 to 11 (B) Please give test string: wizzard:c graham$ */ Learn about this subject
This module and example are covered on the following public courses:
* Learning to Program in C * Learning to program in C and C++ * Programming in C * C and C++ Programming * Learning to program in C and C++ * C and C++ Programming Also available on on site courses for larger groups Books covering this topic
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Other Examples
This example comes from our "Character Strings" training module. You'll find a description of the topic and some
other closely related examples on the "Character Strings" module index page.
Full description of the source code
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