How do I write file modification dates programmatically in POSIX?

Question

I would like to touch my files from C code to modify their access date. This does not seem to work:

struct stat fileSt;
lstat(path, &fileSt);
fileSt.st_mtime = time(NULL);

Thank you for help.

Answer 1

The old utime() and utimes() are OK for many use-cases, but to update atime & mtime with nanosecond resolution, which you need on modern systems, use:

utimensat(0, path, NULL, 0);

This is very useful in combination with newer stat() which returns a struct timespec st_mtim field in struct stat with nanosecond resolution as well.