Programming

hi, I need to know how to lock a file. I used the following code, but after executing the program the file 'write.txt' remined empty, and I have no idea why.Maybe I'm not using the corresponding syntax for blocking a file. But I deleted then the blocking part and the problem persisted.
see to code:
......
f=open("read.txt",O_RDONLY);
fcntl(f,F_SETLK);
read(f,buffer,sizeof(buffer));
g=open("write.txt",O_WRONLY);
write(g,buffer,sizeof(buffer));
close(g);
fcntl(f,F_UNLCK);
close(f);
.......
then I tried to replace open with fopen (so I use FILE *g of course, and fprintf()) but still nothing was in that file(write.txt).So I have no clue. If you got sometime pls say somethin'. I need to do this as soon as I can. You are welcomed to say somethin' smart
10x

I think you mean lock a file.

Try creating a file with stuff in it to start with

Code:

echo "now my file has stuff in it" > write.txt

fcntl(filedescriptor, F_SETLK, struct *flock ) three (3) arguments are required to make fcntl work for locking.

Note - a lot of unix kernels do not support mandatory locking. This means that anybody who breaks the rules (like your code is doing) will still be able to stomp on somebody else's file. Regardless of fcntl. In other words, locking depends on each C module playing by the rules.

Read the C example at the end of this page:

http://www.opengroup.org/onlinepubs/...ons/fcntl.html