Can bit fields be structure / union fields, never “normal”, “autonomous” variables?

Question

The field portion of bit fields seems to suggest that they can only be fields within a structure or union.

Can a bit field be a typical "autonomous" variable, outside of any aggregate data type, such as a union or structure, as follows:

   int sum:6;   //Can this work as a declaration statement?
   sum=4;

If not, why? If bit fields are mainly designed to use less memory, why can't we declare any variable as a bit field if we know that it will not exceed this size?

Answer 1

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C99:

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6.7

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6.7.2.1 .

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Answer 2

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int num = 9;
int fourthBit = (num >> 4) & 1;

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: http://msdn.microsoft.com/en-us/library/yszfawxh(v=vs.80).aspx

Answer 3

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