how to reach the bytes of a number? and why? C

Question

I know that in order to reach the bytes of a number we should do:

unsigned int number=value;
char* bytes = (char*)&number;

...but I don't really understand why.

Why do we need to use char *? Why are we casting here?

Thank you :)

I don't understand why we use char *? why dont we use int *? — Dvir Samuel, Oct 23 '15 at 13:15
a char is a byte, and I dont know why "we" use anything, as what you posted is not real code and certainly not a full program — Magisch, Oct 23 '15 at 13:15
Because an `int * ` points to an `int`, which is bigger than a byte. — Mike Kinghan, Oct 23 '15 at 13:16
@user3169750 Basically this type of casting to find out endianess but certainly not this much code. There is more to it . — ameyCU, Oct 23 '15 at 13:17
@user3169750 The size of a `char` is 1 byte because the C Standard defines it so. — Mike Kinghan, Oct 23 '15 at 13:19

score 1 · Answer 1 · edited May 23 '17 at 12:23

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Not entirely sure what your problem is here.

Why do we need to use char *?

A char is a byte (read: 8 binary numbers 0 or 1) that can represent a decimal value from 0-255 or -128 - +127 in signed form. It is by default signed.

an int is bigger then a byte, hence the need to cast it to get a byte.

Not sure without the context why you'd want to, but you can use that to determine endianness. Related SO Question

edited May 23 '17 at 12:23

Community

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answered Oct 23 '15 at 13:26

Magisch

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it is by default whaterver your compiler says it is. on some platforms, char is by default unsigned. – Tom Tanner Oct 23 '15 at 13:35

score 1 · Answer 2 · answered Oct 23 '15 at 13:28

If you want to get to the bytes of an int, you need a pointer that points at something the size of a byte. A char is defined as the size of a byte, so a pointer to a char lets you get the individual bytes of an int.

int a[10]
int *p_int= &a[0];
p_int++;

The p_int++ increments the variable by the size of an int and so will point to a[1]. It increments with 4 bytes.

char *p_char= (char *)&a[0];
p_char++;

The p_char++ increments the variable by the size of a char and so will point to the second byte of the integer a[0].

how to reach the bytes of a number? and why? C

2 Answers2