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Editorial Team
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Asked: 2026-06-09T02:08:29+00:00

This is question about Objective-C. I wrote the program that uses regular expression with

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This is question about Objective-C. I wrote the program that uses regular expression with getting whole HTML. I have uploaded the program to GitHub. However, exception occurs.

The purpose of this program is to get the “og:image” by regular expression match. This is the image which is displayed by writing URL in Facebook. To set this image, you write in HTML as below:

<meta property="og:image"
content="http://business.nikkeibp.co.jp/article/NBD/20120727/235043/zu1.jpg">

So I wrote the program which get whole HTML and find og:image part. The code is below:

// Web page address
NSURL *url = [NSURL URLWithString:textField.text];

// Get the web page HTML
NSString *string = 
[NSString stringWithContentsOfURL:url encoding:NSUTF8StringEncoding error:nil];

// prepare regular expression to find text
NSError *error   = nil;
NSRegularExpression *regexp =
[NSRegularExpression regularExpressionWithPattern:
 @"<meta property=\"og:image\" content=\".+\""
                                          options:0
                                            error:&error];

@try {
    // find by regular expression
    NSTextCheckingResult *match =
    [regexp firstMatchInString:string options:0 range:NSMakeRange(0, string.length)];

    // get the first result
    NSRange resultRange = [match rangeAtIndex:0];
    NSLog(@"match=%@", [string substringWithRange:resultRange]); 

    if (match) {

        // get the og:image URL from the find result
        NSRange urlRange = NSMakeRange(resultRange.location + 35, resultRange.length - 35 - 1);
        NSURL *urlOgImage = [NSURL URLWithString:[string substringWithRange:urlRange]];
        imageView.image = [UIImage imageWithData:[NSData dataWithContentsOfURL:urlOgImage]];
    }
}

The whole code is in GitHub as below:

https://github.com/weed/p120728_GetOgImage/blob/master/GetOgImage/ViewController.m

However, sometimes this program through exception.

Screen shots is here: https://github.com/weed/p120728_GetOgImage/blob/master/readme.md

Why exception occurs? Please teach me. Thank you for your help.

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1 Answer

  1. Editorial Team

    My friend kindly pointed about considering Character Encoding. The character encoding of first URL page is UTF-8, and the second one is EUC-JP.

    With the code below I could get the og:image of second URL I showed above.

    - (NSString *)encodedStringWithContentsOfURL:(NSURL *)url
{
    // Get the web page HTML
    NSData *data = [NSData dataWithContentsOfURL:url];

    // response
    int enc_arr[] = {
        NSUTF8StringEncoding,           // UTF-8
        NSShiftJISStringEncoding,       // Shift_JIS
        NSJapaneseEUCStringEncoding,    // EUC-JP
        NSISO2022JPStringEncoding,      // JIS
        NSUnicodeStringEncoding,        // Unicode
        NSASCIIStringEncoding           // ASCII
    };
    NSString *data_str = nil;
    int max = sizeof(enc_arr) / sizeof(enc_arr[0]);
    for (int i=0; i<max; i++) {
        data_str = [
               [NSString alloc]
               initWithData : data
               encoding : enc_arr[i]
               ];
        if (data_str!=nil) {
               break;
        }
    }
    return data_str;    
}

    I made the check library of character encoding named NSString+Encode. The whole code is in GitHub:

    https://github.com/weed/p120728_OgImageLibrary

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