将 NSString 字符串转换成 Unicode 编码（形如 \u597d）

gistfile1.m

+ (NSString *)unicodeStringWithString:(NSString *)string {
    NSString *result = [NSString string];
    for (int i = 0; i < [string length]; i++) {
        result = [result stringByAppendingFormat:@"\\u%04x", [string characterAtIndex:i]];
        /*
         因为 Unicode 用 16 个二进制位（即 4 个十六进制位）表示字符,对于小于 0x1000 字符要用 0 填充空位,
         所以使用 %04x 这个转换符, 使得输出的十六进制占 4 位并用 0 来填充开头的空位.
         */
    }
    return result;
}

+ (NSString *)stringWithUnicodeString:(NSString *)string {
    NSArray *strArray = [[string substringFromIndex:2] componentsSeparatedByString:@"\\u"];
    NSString *result = [NSString string];
    for (NSString *str in strArray) {
        NSString *tmpStr = [@"0x" stringByAppendingString:str];
        unichar c = strtoul([tmpStr UTF8String], 0, 0);
        /*
         上面两行也可以写成下面一行：
         unichar c = strtoul([str UTF8String], 0, 16);
         */
        result = [result stringByAppendingString:[NSString stringWithCharacters:&c length:1]];
    }
    return result;
}