add example to write a file using a file descriptor.

1 files changed, 68 insertions, 0 deletions

diff --git a/simplenote.c b/simplenote.c
new file mode 100644
index 0000000..a89df2c
--- /dev/null
+++ b/simplenote.c
@@ -0,0 +1,68 @@
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <fcntl.h>
+#include <sys/stat.h>
+
+void usage(const char *prog_name, char *filename)
+{
+  printf("Usage: %s <data to add to %s>\n", prog_name, filename);
+  exit(0);
+}
+
+void fatal(char *);
+void *ec_malloc(unsigned int);
+
+int main(int argc, const char *argv[])
+{
+  int fd;
+  char *buffer, *datafile;
+
+  buffer = (char *) ec_malloc(100);
+  datafile = (char *) ec_malloc(20);
+  strcpy(datafile, "/tmp/notes");
+
+  if (argc < 2)
+    usage(argv[0], datafile);
+
+  strcpy(buffer, argv[1]);
+  printf("[DEBUG] buffer @ %p: \'%s\'\n", buffer, buffer);
+  printf("[DEBUG] datafile @ %p: \'%s\'\n", datafile, datafile);
+
+  strncat(buffer, "\n", 1);
+
+  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);
+
+  if (write(fd, buffer, strlen(buffer)) == -1)
+    fatal("in main() while writing buffer to file");
+
+  if(close(fd) == -1)
+    fatal("in main() while closing file");
+
+  printf("note has been saved.\n");
+  free(buffer);
+  free(datafile);
+  return 0;
+}
+
+void fatal(char *message)
+{
+  char error_message[100];
+  strcpy(error_message, "[!!] Fatal Error ");
+  strncat(error_message, message, 83);
+  perror(error_message);
+  exit(-1);
+}
+
+void *ec_malloc(unsigned int size)
+{
+  void *ptr;
+  ptr = malloc(size);
+  if (ptr == NULL) 
+    fatal("in ec_malloc() on memory allocation");
+  return ptr;
+}