clearerr

#include <stdio.h>
#include <assert.h>
 
int main(void)
{
 FILE * tmpf = tmpfile ();
 fputs ("cppreference.com\n", tmpf);
 rewind (tmpf);
 
 for (int ch; (ch = fgetc (tmpf)) != EOF ; putchar (ch)) { }
 
 assert (feof (tmpf)); // the loop is expected to terminate by EOF
 puts ("End of file reached");
 
 clearerr(tmpf); // clear EOF
 
 puts (feof (tmpf) ? "EOF indicator set" 
 : "EOF indicator cleared");
}

cppreference.com
End of file reached
EOF indicator cleared