Graphics Programs Reference
In-Depth Information
strcpy(buffer, argv[1]); // Copy into buffer.
printf("[DEBUG] buffer @ %p: \'%s\'\n", buffer, buffer);
printf("[DEBUG] datafile @ %p: \'%s\'\n", datafile, datafile);
strncat(buffer, "\n", 1); // Add a newline on the end.
// Opening 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);
// Writing data
if(write(fd, buffer, strlen(buffer)) == -1)
fatal("in main() while writing buffer to file");
// Closing file
if(close(fd) == -1)
fatal("in main() while closing file");
printf("Note has been saved.\n");
free(buffer);
free(datafile);
}
// A function to display an error message and then exit
void fatal(char *message) {
char error_message[100];
strcpy(error_message, "[!!] Fatal Error ");
strncat(error_message, message, 83);
perror(error_message);
exit(-1);
}
// An error-checked malloc() wrapper function
void *ec_malloc(unsigned int size) {
void *ptr;
ptr = malloc(size);
if(ptr == NULL)
fatal("in ec_malloc() on memory allocation");
return ptr;
}
Besides the strange-looking flags used in the
open()
function, most of this
code should be readable. There are also a few standard functions that we
haven't used before. The
strlen()
function accepts a string and returns its
length. It's used in combination with the
write()
function, since it needs to
know how many bytes to write. The
perror()
function is short for
print error
and is
used in
fatal()
to print an additional error message (if it exists) before exiting.
reader@hacking:~/booksrc $ gcc -o simplenote simplenote.c
reader@hacking:~/booksrc $ ./simplenote
Usage: ./simplenote <data to add to /tmp/notes>
