Ah so you save it as an ASCII string? Hm I wouldn’t recommend that, since ASCII strings are variable length and you have to detect the 0 at the end… if you store it directly as the binary representation, constant-width, and directly in the right endianness (little-endian, “backwards”) you will have much less trouble.
So if replace the node_id.bin file with hexadecimal content
05 00 00 00
it will read is little-endian number 5, without any code changes.
The code you have now reads a 4-byte value (uint32_t) from that memory location but you only prepared 1 byte of character data to it – you would have to change uint32_t node_id = 0; to char node_id = 0; and print it with %c if you’d want it to work with that .bin file. For larger than 1 character node-ids that will ofc not work, so you would need to build additional logic for reading multiple bytes and detecting the end…
So as said, better to use constant-width binary integer. After reading it out, you can still directly convert it to a String if you need it.