Le 26/07/2017 à 22:00, Christopher Clements a écrit :
Wouldn't this work? (no error checking of course XD)
off_t lseek(int fd, off_t offset, int whence);
ssize_t write(int fd, const void *buf, size_t count);
ssize_t pwrite(int fd, const void *buf, size_t count, off_t
offset) {
lseek(fd, offset, SEEK_SET);
return write(fd, buf, count);
}
I looked at the source code of Musl libc. Actually both write() and
pwrite() are simple wrappers to... a general-purpose system-call
wrapper. The second simply has one more argument. I didn't dig further.
At first glance at least, it means that file offsets are managed in the
kernel or VFS but they can be bypassed by pwrite(). AFAIR pwrite()
doesn't change the "current" file offset; it simply ignores and bypasses
it, which isn't exactly what your example does.
But the discussion was about low-level vs high-level programming.
Using unistd's read() and write() in C means you are dealing with low
level issues; otherwise why would you bother with the complexity it
introduces - not only you need to deal with buffering but also with
retries when interrupted by signals.
Didier
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