Regarding the 16 bit enumeration in c lang

jyothidamu · 03-22-2011, 06:29 PM

enum argu {
send = 0x0001
, receive = 0x0002

};

can any one explain what is the meaning of the 0x0001 and 2. i am very glad if any one can explain with example

dwhitney67 · 03-22-2011, 06:50 PM

0x0001 is the hexadecimal equivalent of the value of 1. I'll let you guess what 0x0002 is.

As for the enumerated identifiers, they were chosen to uniquely identify a value. Thus "send" is 0x0001 and "receive" is 0x0002. Whether these numbers actually mean anything, or were arbitrarily chosen, cannot be deduced from the code snip you provided.

Note, when an enumerated list is defined, if the first identifier is not assigned a value, then it will be assigned the default value of zero; all subsequent identifiers will have a value of one more than the previous, unless specifically assigned a value. For example:

Code:

enum Foo
{
   ZERO,           // has the value of 0
   APPLE,          // has the value of 1
   ORANGE = 3,     // obviously has value of 3
   TOMATO,         // has the value of 4
   ZUCCHINI = 6    // obviously has value of 6
};

Enumerated values are not 16-bit values, but instead allocated a full 32-bits (4 bytes). See for yourself on your system using this program:

Code:

#include <stdio.h>

enum Foo
{
   ZERO,
   ONE
};

int main()
{
   printf("sizeof(ZERO) = %u\n", sizeof(ZERO));
   return 0;
}

Sergei Steshenko · 03-22-2011, 07:44 PM

Quote:

Originally Posted by jyothidamu

enum argu {
send = 0x0001
, receive = 0x0002

};

can any one explain what is the meaning of the 0x0001 and 2. i am very glad if any one can explain with example

The answer is (at least) twofold:

in C99 standard ( http://www.open-std.org/JTC1/SC22/wg...docs/n1124.pdf ) look for 'hexadecimal';
if you do not know what hexadecimal in particular and radix in general are, read http://en.wikipedia.org/wiki/Radix .

jyothidamu · 03-23-2011, 04:31 AM

Quote:

Originally Posted by dwhitney67

0x0001 is the hexadecimal equivalent of the value of 1. I'll let you guess what 0x0002 is.

As for the enumerated identifiers, they were chosen to uniquely identify a value. Thus "send" is 0x0001 and "receive" is 0x0002. Whether these numbers actually mean anything, or were arbitrarily chosen, cannot be deduced from the code snip you provided.

Note, when an enumerated list is defined, if the first identifier is not assigned a value, then it will be assigned the default value of zero; all subsequent identifiers will have a value of one more than the previous, unless specifically assigned a value. For example:

Code:

enum Foo
{
   ZERO,           // has the value of 0
   APPLE,          // has the value of 1
   ORANGE = 3,     // obviously has value of 3
   TOMATO,         // has the value of 4
   ZUCCHINI = 6    // obviously has value of 6
};

Enumerated values are not 16-bit values, but instead allocated a full 32-bits (4 bytes). See for yourself on your system using this program:

Code:

#include <stdio.h>

enum Foo
{
   ZERO,
   ONE
};

int main()
{
   printf("sizeof(ZERO) = %u\n", sizeof(ZERO));
   return 0;
}

what is the use of Hexadecimal values these numbers are arbitrarily chosen and thanks for the good explanation

dwhitney67 · 03-23-2011, 06:42 AM

Quote:

Originally Posted by jyothidamu

what is the use of Hexadecimal values these numbers are arbitrarily chosen and thanks for the good explanation

I'm not sure if this is a question... but oftentimes, hex values are used in lieu of decimal because it makes them easier to read. All numbers within a computer are stored in binary, thus the use of hex or even base-10 numbers serves no purpose other than to gratify humans, who both develop and read, code.

Sergei Steshenko · 03-23-2011, 11:00 AM

Quote:

Originally Posted by jyothidamu

what is the use of Hexadecimal values these numbers are arbitrarily chosen ...

It depends. I.e. if a program is to deal with an HW controller, the numbers are to be values to be written the HW controller control register.

If you convert the numbers into binary, you'll see that in your case both number have just one bit set.

MTK358 · 03-23-2011, 08:21 PM

Quote:

Originally Posted by jyothidamu

enum argu {
send = 0x0001
, receive = 0x0002

};

can any one explain what is the meaning of the 0x0001 and 2. i am very glad if any one can explain with example

Those aren't 16-bit numbers. Those zeros just mean nothing, maybe they're to align the code or make it look nicer. You could write 0x1 or 0x0000000000000001 and it would mean the same thing to the compiler.

Peverel · 04-18-2011, 05:46 PM

Hexadecimal is used because these are masks for bits. Very long ago I wrote some assembler routines that did serial input/output directly, inputting or outputing characters. There was a data register and a status register, the last bit of the status register was set if a character was still being sent, the previous one if a character had been received but not processed. To send a string, one sent the first character to the data register, waited till the last bit was unset, then sent the next and so on. Similarly with input. To see if a character had just been received, one loaded "receive" to a register, logical anded it with the status register: if the result was non-zero, one could copy the resultant character from the input data register, which would reset the status bit ready for the next character to be received.

theNbomr · 04-18-2011, 06:13 PM

Quote:

Originally Posted by dwhitney67

I'm not sure if this is a question... but oftentimes, hex values are used in lieu of decimal because it makes them easier to read. All numbers within a computer are stored in binary, thus the use of hex or even base-10 numbers serves no purpose other than to gratify humans, who both develop and read, code.

Also, since each hex digit represents exactly 4 bits, it is almost trivial to create code in very low-level languages like assembler to convert numbers to their human-readable ASCII format as hexadecimal. Same for octal. Converting to ASCII in a decimal radix is comparatively difficult to code, requires larger code and is slower.

--- rod.