Thread: looking to use sizeof for enum?

  1. #1
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    looking to use sizeof for enum?

    I have a type enum and would like to use the sizeof command to get a value....Can I do this? For instance my enum is:

    Code:
    typedef enum {EMPTY, RST, PWM_DIV, PWM_DUTYCYCLE, DAC_REF, ADC_SAMP_TIME = 8, ADC_NUM_SAMPLES, ADC_CONV} commands
    I would like to do sizeof(commands) and get back 8....if I run as is I get back 2 which presumably is the size of a type enum

    Thanks

  2. #2
    C++ Witch laserlight's Avatar
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    sizeof won't do what you want since commands is a type rather than some kind of aggregate. Since you're explicitly assigning a value in the middle, you cannot use the trick of computing from the value of the last enumerator either. Why do you need to know this count? Maybe there is another way that does not rely on such knowledge.
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  3. #3
    and the hat of int overfl Salem's Avatar
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    Well if you don't mess up the numbering with an assignment, you typically do this.
    Code:
    typedef enum {EMPTY, RST, PWM_DIV, PWM_DUTYCYCLE, DAC_REF, ADC_SAMP_TIME, ADC_NUM_SAMPLES, ADC_CONV, CMD_LAST} commands
    CMD_LAST will be the number of elements that precede it.
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  4. #4
    Registered User awsdert's Avatar
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    Quote Originally Posted by ridgerunnersjw View Post
    I have a type enum and would like to use the sizeof command to get a value....Can I do this? For instance my enum is:

    Code:
    typedef enum {EMPTY, RST, PWM_DIV, PWM_DUTYCYCLE, DAC_REF, ADC_SAMP_TIME = 8, ADC_NUM_SAMPLES, ADC_CONV} commands
    I would like to do sizeof(commands) and get back 8....if I run as is I get back 2 which presumably is the size of a type enum

    Thanks
    From what I see I think you're misunderstanding what sizeof does, for starters sizeof(commands) will, in general, be equal to sizeof(int), that is the sizeof of what will contain the values of your enums, not the count of them. Secondly to get the count you could do something as simple as this:

    Code:
    typedef enum
    {
    	EMPTY = 0,
    	RST,
    	PWM_DIV,
    	PWM_DUTYCYCLE,
    	DAC_REF,
    	ADC_SAMP_TIME = 8,
    	ADC_NUM_SAMPLES,
    	ADC_CONV,
    	LAST_CMD_MARKER,
    	CMD_COUNT = DAC_REF + (LAST_CMD_MARKER - SAMP_TIME)
    } commands;
    Might be 1 off with the count, I didn't bother with a math check since it was off the top of my head, can just add - 1 to the end if it is, anyways CMD_COUNT would then hold what you were looking for.

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