Question

If I have the string “Hello World”, is it possible to use NSRegularExpression with the pattern @”World” to get the position of the match, i.e. in the “Hello World” example the position/index of the match should be “6”?

in php I’d use preg_match with the “PREG_OFFSET_CAPTURE” flag to achieve this, does objective-c support this?

Answer 1

You can do it the Cocoa way:

NSRegularExpression *regex = [[NSRegularExpression alloc] initWithPattern:@"world" options:0 error:NULL];
// omitted error checking for the sake of simplicity
NSString *str = @"Hello world!";
[regex enumerateMatchesInString:str
    options:0
    range:NSMakeRange(0, str.length)
    usingBlock:^(NSTextCheckingResult *result, NSMatchingFlags flags, BOOL *stop)
    {
        NSLog(@"Match at [%d, %d]", result.range.location, result.range.length);
    }];
[regex release];

Or the POSIX way (this may be convenient for you, since you want only one match, and this function/method returns the match range directly):

#include <regex.h>

- (NSRange)matchString:(NSString *)string toRegex:(NSString *)regex
{
    regex_t regex_obj;
    regmatch_t match;
    const char *regex_str;
    const char *match_str;
    int error;

    regex_str = [regex UTF8String];
    error = regcomp(&regex_obj, regex_str, REG_EXTENDED);
    if (error)
    {
        return NSMakeRange(NSNotFound, 0);
    }

    match_str = [string UTF8String];
    error = regexec(&regex_obj, match_str, 1, &match, 0);
    if (error)
    {
        return NSMakeRange(NSNotFound, 0);
    }

    regfree(&regex_obj);
    return NSMakeRange(match.rm_so, match.rm_eo - match.rm_so);
}