Why is 0x00000100 = 256?

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Shouldn't 0x00000100 = 4.

I understand that 0x00000001 = 1 since 2^0 and 0x00000010 = 2 since 2^1. What is wrong with my thinking?

initVariable(&variable1, "variable1", "1, 2, 3", 0x00000100);

assertIntegerEquals(variable1.address, 4); // 0x00000100 = 4?

My assertion fails because it says that 256 != 4

c
binary
asked on Stack Overflow Nov 20, 2013 by Wang-Zhao-Liu Q

6 Answers

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Numbers that begin with 0x are interpreted as hexadecimal (base 16) in C.

So 0x10 == 16, and 0x100 == 256, 0x10000 == 65536, etc.

Powers of two are:

  • 20 = 0x1
  • 21 = 0x2
  • 22 = 0x4
  • 23 = 0x8
  • 24 = 0x10
  • 25 = 0x20
  • 26 = 0x40
  • 27 = 0x80
  • 28 = 0x100
answered on Stack Overflow Nov 20, 2013 by Dietrich Epp • edited Sep 27, 2019 by S.S. Anne
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No, the 0x means hexadecimal (i.e. base-16) and not binary, which is what you seem to be confusing it with.

If you want to use binary literals in your code, then see this SO question, which mentions the gcc extension that allows 0b00000100 to be used to represent 4 in binary.

answered on Stack Overflow Nov 20, 2013 by trojanfoe • edited May 23, 2017 by Community
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0x00000100 is in base-16 because 0x prefix means you are using hexadecimal notation.

So 0x00000001 = 1*160 = 1, 0x00000010 = 1*161, 0x00000100 = 1*162 = 256 and 0x00000123 = 1*162 + 2*161 + 3*160 = 256 + 32 + 3 = 291

To play with base-2, base-10 and base-16 notation, you can try this site: http://www.mathsisfun.com/binary-decimal-hexadecimal-converter.html

answered on Stack Overflow Nov 20, 2013 by Korchkidu • edited Nov 20, 2013 by Korchkidu
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The 0x prefix means hexadecimal

answered on Stack Overflow Nov 20, 2013 by Basile Starynkevitch
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0x00000100 (hex) = 0000 0000 0000 0000 0000 0001 0000 0000 (binary) = 256 (decimal)

answered on Stack Overflow Nov 20, 2013 by Fiddling Bits
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0x prefix is hexadecimal 0x00000100 = 256 base 16

00000100 = 00000120100

= 1 * 162 + 0*161 + 0*0

=1 * 256 + 0*16 + 0*1

= 256 + 0 + 0

=256

answered on Stack Overflow Sep 24, 2015 by shas

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