How can I copy a file on Unix using C?

Question

I'm looking for the Unix equivalent of Win32's CopyFile, I don't want to reinvent the wheel by writing my own version.

Answer 1

There is no need to either call non-portable APIs like sendfile, or shell out to external utilities. The same method that worked back in the 70s still works now:

#include <fcntl.h> #include <unistd.h> #include <errno.h>  int cp(const char *to, const char *from) {     int fd_to, fd_from;     char buf[4096];     ssize_t nread;     int saved_errno;      fd_from = open(from, O_RDONLY);     if (fd_from < 0)         return -1;      fd_to = open(to, O_WRONLY | O_CREAT | O_EXCL, 0666);     if (fd_to < 0)         goto out_error;      while (nread = read(fd_from, buf, sizeof buf), nread > 0)     {         char *out_ptr = buf;         ssize_t nwritten;          do {             nwritten = write(fd_to, out_ptr, nread);              if (nwritten >= 0)             {                 nread -= nwritten;                 out_ptr += nwritten;             }             else if (errno != EINTR)             {                 goto out_error;             }         } while (nread > 0);     }      if (nread == 0)     {         if (close(fd_to) < 0)         {             fd_to = -1;             goto out_error;         }         close(fd_from);          /* Success! */         return 0;     }    out_error:     saved_errno = errno;      close(fd_from);     if (fd_to >= 0)         close(fd_to);      errno = saved_errno;     return -1; }