Graphics Programs Reference
In-Depth Information
}
void fatal(char *); // A function for fatal errors
void *ec_malloc(unsigned int); // An error-checked malloc() wrapper
int main(int argc, char *argv[]) {
int userid, fd; // File descriptor
char *buffer, *datafile;
buffer = (char *) ec_malloc(100);
datafile = (char *) ec_malloc(20);
strcpy(datafile, "/var/notes");
if(argc < 2) // If there aren't command-line arguments,
usage(argv[0], datafile); // display usage message and exit.
strcpy(buffer, argv[1]); // Copy into buffer.
printf("[DEBUG] buffer @ %p: \'%s\'\n", buffer, buffer);
printf("[DEBUG] datafile @ %p: \'%s\'\n", datafile, datafile);
// Opening the file
fd = open(datafile, O_WRONLY|O_CREAT|O_APPEND, S_IRUSR|S_IWUSR);
if(fd == -1)
fatal("in main() while opening file");
printf("[DEBUG] file descriptor is %d\n", fd);
userid = getuid(); // Get the real user ID.
// Writing data
if(write(fd, &userid, 4) == -1) // Write user ID before note data.
fatal("in main() while writing userid to file");
write(fd, "\n", 1); // Terminate line.
if(write(fd, buffer, strlen(buffer)) == -1) // Write note.
fatal("in main() while writing buffer to file");
write(fd, "\n", 1); // Terminate line.
// Closing file
if(close(fd) == -1)
fatal("in main() while closing file");
printf("Note has been saved.\n");
free(buffer);
free(datafile);
}
The output file has been changed from /tmp/notes to /var/notes, so the
data is now stored in a more permanent place. The
getuid()
function is used to
get the real user ID, which is written to the datafile on the line before the note's
line is written. Since the
write()
function is expecting a pointer for its source,
the
&
operator is used on the integer value
userid
to provide its address.
