How can a file contain null bytes?

Question

How is it possible that files can contain null bytes in operating systems written in a language with null-terminating strings (namely, C)?

For example, if I run this she

Answer 1

Consider the usual C function calls for writing data to files — write(2):

ssize_t
write(int fildes, const void *buf, size_t nbyte);

… and fwrite(3):

size_t
fwrite(const void *restrict ptr, size_t size, size_t nitems, FILE *restrict stream);

Neither of these functions accept a const char * NUL-terminated string. Rather, they take an array of bytes (a const void *) with an explicit size. These functions treat NUL bytes just like any other byte value.