Not understanding fwrite() and ints

[tame gulch]

hi so im getting sooo fucking confused with smth. here is my code

    unsigned int magic_word_array[] = {0x54, 0x41, 0x42, 0x49};
    fwrite(magic_word_array, sizeof(char), MAGIC_SIZE, out_file);

this is writing 0x54 0x00 0x00 0x00 to the file, why?

[finite sandal]

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[sweet socket]

what's magic_size

[barren topaz]

Your magic array was likely supposed to contain chars/unsigned chars, no?

[sweet socket]

i'm guessing your magic_size is 4, so it only writes the first int

if you wanted to write ints maybe sizeof(char) was supposed to be sizeof(int)

[tame gulch]

4

yee, well, if i just change it to unsigned char it works

but im a bit confused and its relevant to the rest of my code

why doesnt fwrite work similarly to smth like fputc? where if i have a unsigned int, itll just use the last 8 bytes of it? or is my understadnginflawed there too

[sweet socket]

you are giving it a pointer

[tame gulch]

AH

wait i think i get you

so itll be like

00 00 00 54 00 00 00 41 00 00 00 42 00 00 00 49

so itll start at 54, and then sizeof(char) = 1 byte so itll move along one byte which will just go to 00?

[sweet socket]

yep

[tame gulch]

hm

then why does

unsigned int magic_word_array[] = {0x54, 0x41, 0x42, 0x49};
fwrite(magic_word_array, sizeof(unsigned int), MAGIC_SIZE, out_file);

do 54 00 00 00 41 00 00 00 42 00 00 00 49 in the file?

ah

that also makes sense now thinking about it

[tawny quest]

Endianness

[uncut lichen]

like rhubarb said - x86 is little endian, which means the "littlest" or least significant byte goes on the left end

thus short int of value 1 is stored in memory as "01 00"

and 256 is "00 01", i.e. you would write it in code as 0x100, but in memory bytes are stored in reverse order

(in case "left end" is vague, it is smaller address in memory)