No it's not, write is wayyyy slower. I just did a test, I write "hello\n" to a file 10,000,000 times. Using fprintf() and stdio.h, it takes 0.04s on my machine. Using write(), it takes 7.6s, over 2 orders of magnitude slower.

Syscalls are extremely expensive and dominant the execution time unless you are writing large chunks of data all at once. Which is precisely why stdio.h exists, because it only occasionally flushes the buffer with write(). This can be observed when you get a segfault, often it seems like your print statements did not execute. One can use fflush() to force stdio.h to flush the buffer.

write() on the otherhand, always writes the data, well, at least to the file buffer cache. fsync() is required to ensure that the data is on disk, though I've seen systems lie about that too.