Thread: Using uchar for uint8?

  1. 04-20-2009 #1
    Witchfinder
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    Using uchar for uint8?

    Hello,

    Is it correct to use uchar for uint8 values as they are both unsigned, and 8 bit?

    Instead of getting 2005 I'm getting 8224. Thats using &u. I don't think any byte ordering is required.

    I'm also using:
    ushort for uint16
    UINT32 for uint32
    UCHAR for dstring < works

    I'm programming scsi commands to return data from a dvd disc. Sector 16 ISO PVD.
    UDF 1.02 Spec:
    Code:
    struct timestamp { /* ISO 13346 1/7.3 */
Uint16 TypeAndTimezone;
Uint16 Year;
Uint8 Month;
Uint8 Day;
Uint8 Hour;
Uint8 Minute;
Uint8 Second;
Uint8 Centiseconds;
Uint8 HundredsofMicroseconds;
Uint8 Microseconds;
}
    C code:
    Code:
        typedef struct _timestamp { /* ECMA 167 1/7.3 */
    USHORT TypeAndTimezone;
    USHORT Year;
    UCHAR Month;
    UCHAR Day;
    UCHAR Hour;
    UCHAR Minute;
    UCHAR Second;
    UCHAR Centiseconds;
    UCHAR HundredsofMicroseconds;
    UCHAR Microseconds;
    }
    Returned:
    Type and timezone: 8224
    Year: 8224
    Month:32
    Day: 32
    Hour:32
    Min:32
    Sec:32 etc

    Thanks for any help!
    Last edited by Witchfinder; 04-20-2009 at 11:37 AM.
  2. 04-20-2009 #2
    bithub
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    In this case byte ordering can't possibly matter. 8224 is 0x2020, so the 2 bytes are the same. If you change the types back to what Microsoft has defined, does the function work as expected?
    [edit]I am assuming this is Windows based code. This may not be the case though. [/edit]
  3. 04-20-2009 #3
    Witchfinder
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    I don't think there is an "uint16" data type. Windows Data Types (Windows)

    I ecma spec says:
    16-bit unsigned numerical values
    A Uint16 value, represented by the hexadecimal representation #wxyz, shall be recorded in a two-byte field as
    #yz #wx.
    NOTE
    For example, the decimal number 4 660 has #1234 as its hexadecimal representation and shall be recorded as
    #34 #12.

    MSDN:
    SHORT: A 16-bit integer. The range is –32768 through 32767 decimal.
    USHORT: Unsigned SHORT. The range is 0 through 65535 decimal.
  4. 04-20-2009 #4
    wyliek
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    can you show your code that assigns to the time struct and read back from it?
  5. 04-20-2009 #5
    brewbuck
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    Although a char is not guaranteed to be 8 bits, any platform where it isn't is so different from the usual that almost all of your code would have to change anyway.

    I'd just specify in the requirements that a supported platform must have 8 bit characters, and use unsigned char as the type for "byte"
    Code:
    //try
//{
	if (a) do { f( b); } while(1);
	else   do { f(!b); } while(1);
//}
  6. 04-20-2009 #6
    Witchfinder
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    Forgot to say its just for windows xp. It seems to return data correctly otherwise text like "Jaws" or "Deluxe Digital Studio" wouldn't display. If I change one of the data types from its correct big length to something else the program crashes, thus I think all the field lengths are correct. Only thing I can thing of is the data types making it incorrect.
  7. 04-20-2009 #7
    laserlight
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    I suppose that if you wanted to make sure that users pay attention to the requirements, you could assert(CHAR_BIT == 8 && "Library requires 8 bit bytes") in the appropriate places.
    Quote Originally Posted by Bjarne Stroustrup (2000-10-14)
    I get maybe two dozen requests for help with some sort of programming or design problem every day. Most have more sense than to send me hundreds of lines of code. If they do, I ask them to find the smallest example that exhibits the problem and send me that. Mostly, they then find the error themselves. "Finding the smallest program that demonstrates the error" is a powerful debugging tool.
    Look up a C++ Reference and learn How To Ask Questions The Smart Way
  8. 04-20-2009 #8
    wyliek
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    It looks like the timestamp struct is un-initialized or has been written to incorrectly. It just seems to be a block of 0x20202020202020

    try initializing the values to some other pattern, then pass to the device IOCTL and see if the values are modified.

    Also, I saw your code pasted here for a short while then it disappeared?
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