Adding new records to a file using a pointer

My program is to get 5 fields, including one called 'position' that shows the sequential position of the record in the file. If I have 5 records in the file, *.txt, the last position in that file should be 4. If i want to put a new record in it should be position 5. After I use f_open to open the file, I am not sure whether to use f_seek or f_read or both. How can I tell the pointer to point to the last record in the file to get the value of the last position? I want to use that plus 1 to put in the new data.
thank you.

After you close a file, the last file position is lost. Therefore, you must reset it each time for appending...


FILE *f = fopen(file, "rb+");
fseek(file, 0, SEEK_END);
fwrite(&data, sizeof(someStruct), 1, f);
fclose(f);





FILE *f = fopen(file, "rb");
while(fread(&data, sizeof(someStruct), 1, f))
count++;
fclose(f);