Objective-C

Regular Expression Replace Capture Groups

See more Regular Expressions Examples

Demonstrates replacing capture groups for a regular expression.

Note: Chilkat uses PCRE2. See PCRE2 Regular Expressions
Also see: PCRE2 Performance

Objective-C

#import <NSString.h>
#import <CkoStringBuilder.h>
#import <CkoJsonObject.h>

BOOL success = NO;

NSString *subject = @"John Anders, +_+_+ Mary Robins $$$$";
NSString *pattern = @"(?<first>\\w+)\\s+(?<last>\\w+)";

CkoStringBuilder *sb = [[CkoStringBuilder alloc] init];
[sb Append: subject];

CkoJsonObject *json = [[CkoJsonObject alloc] init];
json.EmitCompact = NO;

int timeoutMs = 2000;
int numMatches = [[sb RegexMatch: pattern json: json timeoutMs: [NSNumber numberWithInt: timeoutMs]] intValue];
if (numMatches < 0) {
    //  Probably an error in the regular expression.
    //  Suggestion: Use AI to help create and/or diagnose regular expressions.
    NSLog(@"%@",sb.LastErrorText);
    return;
}

//  Examine the matches:
NSLog(@"%@",[json Emit]);

//  There are 2 matches:

//  {
//    "named": {
//      "first": 1,
//      "last": 2
//    },
//    "match": [
//      {
//        "group": [
//          {
//            "cap": "John Anders",
//            "idx": 0,
//            "len": 11
//          },
//          {
//            "cap": "John",
//            "idx": 0,
//            "len": 4
//          },
//          {
//            "cap": "Anders",
//            "idx": 5,
//            "len": 6
//          }
//        ]
//      },
//      {
//        "group": [
//          {
//            "cap": "Mary Robins",
//            "idx": 19,
//            "len": 11
//          },
//          {
//            "cap": "Mary",
//            "idx": 19,
//            "len": 4
//          },
//          {
//            "cap": "Robins",
//            "idx": 24,
//            "len": 6
//          }
//        ]
//      }
//    ]
//  }

//  To replace capture groups, write code to examine each capture group within
//  each match, and provide a replacement string.
//  Then call RegexReplace.

//  For example, let's capitalize the first names, and add append "on" to the last name.
//  After doing replacements, we should get:  JOHN Anderson, +_+_+ MARY Robinson $$$$

int firstNameIdx = [[json IntOf: @"named.first"] intValue];
int lastNameIdx = [[json IntOf: @"named.last"] intValue];

CkoStringBuilder *sbTemp = [[CkoStringBuilder alloc] init];

int i = 0;
numMatches = [[json SizeOfArray: @"match"] intValue];
while (i < numMatches) {

    json.I = [NSNumber numberWithInt: i];

    //  The replacement string for the first name will be all uppercase.
    json.J = [NSNumber numberWithInt: firstNameIdx];
    [sbTemp Clear];
    [json StringOfSb: @"match[i].group[j].cap" sb: sbTemp];
    [sbTemp ToUppercase];
    [json UpdateSb: @"match[i].group[j].rep" sb: sbTemp];

    //  Append "on" to the last name.
    json.J = [NSNumber numberWithInt: lastNameIdx];
    [sbTemp Clear];
    [json StringOfSb: @"match[i].group[j].cap" sb: sbTemp];
    [sbTemp Append: @"on"];
    [json UpdateSb: @"match[i].group[j].rep" sb: sbTemp];

    i = i + 1;
}

//  The JSON now has replacement strings:
NSLog(@"%@",[json Emit]);

//  {
//    "named": {
//      "first": 1,
//      "last": 2
//    },
//    "match": [
//      {
//        "group": [
//          {
//            "cap": "John Anders",
//            "idx": 0,
//            "len": 11
//          },
//          {
//            "cap": "John",
//            "idx": 0,
//            "len": 4,
//            "rep": "JOHN"
//          },
//          {
//            "cap": "Anders",
//            "idx": 5,
//            "len": 6,
//            "rep": "Anderson"
//          }
//        ]
//      },
//      {
//        "group": [
//          {
//            "cap": "Mary Robins",
//            "idx": 19,
//            "len": 11
//          },
//          {
//            "cap": "Mary",
//            "idx": 19,
//            "len": 4,
//            "rep": "MARY"
//          },
//          {
//            "cap": "Robins",
//            "idx": 24,
//            "len": 6,
//            "rep": "Robinson"
//          }
//        ]
//      }
//    ]
//  }

//  Call RegexReplace to update the StringBuilder with the replacements.
success = [sb RegexReplace: json];
if (success == NO) {
    NSLog(@"%@",sb.LastErrorText);
    return;
}

NSLog(@"%@",@"Result after doing replacements:");
NSLog(@"%@",[sb GetAsString]);

//  Result after doing replacements:
//  JOHN Anderson, +_+_+ MARY Robinson $$$$