When a number is written as 0x00... what does the x mean

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Suppose I was trying to create a mask in C for bitwise operations, like

uint32_t Mask = 0x00000003;

What does the x mean? I see a lot of numbers written with that 0x format and I don't understand why and have been unable to find an explanation that really makes sense to me, maybe I'm not searching the right thing.

c
bitwise-operators
asked on Stack Overflow Nov 8, 2018 by John Doe

2 Answers

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'0x' means that the number that follows is in hexadecimal. It's a way of unambiguously stating that a number is in hex, and is a notation recognized by C compilers and some assemblers.

answered on Stack Overflow Nov 8, 2018 by Linny
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it means the the number is expressed in hex , base 16 instead of decimal, based 10. For your example it makes no difference

uint32_t Mask = 0x00000003;

since 3 is 3 in both bases

but

uint32_t Mask = 0x00000010;  // '16' in human talk

is quite different from 

uint32_t Mask = 00000010; // '10' in human talk

You will see 

uint32_t Mask = 0x00000003;

when expressing something where the value is a set of bit flags rather than a number (see the name 'mask') since hex maps nicely to a sequence of bits. You might see

uint32_t Mask1 = 0x00000003;
uint32_t Mask2 = 0x00000010;
uint32_t Mask3 = 0x000000C2;

The first one doesnt need 0x but it just looks cleaner

answered on Stack Overflow Nov 8, 2018 by pm100

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