on windows 2008 server,when I use fprintf to write a LAN network share file frequently,sometimes the file pointer jump back: fp = fopen(filename,"a+"); ... while() { ... pos1 = ftell(fp); <====== pos1 == 1000 fprintf(fp,"%s\n",str); pos2 = ftell(fp); <====== pos2 == 800 ... fflush(fp); } At the same time, the file contents will be disordered. The latter record will overrite the previous record. please help to explain it, thanks.