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 $$$$