Hi all, I encounted a write file problem for Fortran 90. I appreciate it a lot if you can help me. I open a file at the beginning of the program. Then everytime I rewind the unit number and write one new line to the first line of the file (the previous data on the first line is replaced). So the total size of the file is very small ~1kb. However, I found the written file does not show the data I wrote during the simulation and only show the data when the program is finished. I do not know what is the problem. The following is the stream of the program. program test open(unit=10, file ='output.dat' ....) loop i = 1, 100 rewind(10) write(10,*)data end loop end program test So during loop, the size of output.dat is always zero and no output until the end of the program. However, I want to check the output during the loop. Does anyone have any idea about this? Thanks in advance.