Question

I have a very simple question regarding file write.

I have this program:

char buf[20];
size_t nbytes;

strcpy(buf, "All that glitters is not gold\n");
fd= open("test_file.txt",O_WRONLY);
write(fd,buf,strlen(buf));
close(fd);

What am confused is when I open the file test_file.txt after running this program I see some characters like ^C^@^@^@^^^@ after the line “All that glitters is not”: Notice that portion of the buf is not written and those characters appear instead. Why is that so?

Answer 1

You’re writing more than 19 chars in that buffer. Once you’ve done that, the behavior of your program is undefined. It could do whatever it wants.

Allocate a large enough buffer. It has to be able to fit all the letters plus a terminating 0 if you need to be able to treat it as a C string.