object - c 在URL中截取特定参数的值

#pragma mark - 获取url特定的参数
-(NSString *) jiexi:(NSString *)CS webaddress:(NSString *)webaddress
{
    NSError *error;
    NSString *regTags=[[NSString alloc] initWithFormat:@"(^|&|\\?)+%@=+([^&]*)(&|$)",CS];
    NSRegularExpression *regex = [NSRegularExpression regularExpressionWithPattern:regTags
                                                                           options:NSRegularExpressionCaseInsensitive
                                                                             error:&error];

    // 执行匹配的过程
    NSArray *matches = [regex matchesInString:webaddress
                                      options:0
                                        range:NSMakeRange(0, [webaddress length])];
    for (NSTextCheckingResult *match in matches) {

        NSString *tagValue = [webaddress substringWithRange:[match rangeAtIndex:2]];  // 分组2所对应的串
        return tagValue;
    }
    return @"";
}