Finish 4.

.gitignore

@@ -50,3 +50,5 @@ modules.order
 Module.symvers
 Mkfile.old
 dkms.conf
+*.swp
+*.swo

4/fileDirectory/chdir.c

@@ -1,6 +1,15 @@
 #include <unistd.h>
+#include <stdio.h>
 
 int main(void) {
-  // TODO
+  if(chdir("/home/eric") < 0) {
+    printf("chdir error\n");
+    return -1;
+  }
+
+  char buf[1024];
+
+  char *pbuf = getcwd(buf, 1024);
+  printf("CWD: %s\n", pbuf);
   return 0;
 }

4/fileDirectory/dev.c

@@ -0,0 +1,26 @@
+#include <sys/stat.h>
+#include <stdio.h>
+#include <sys/types.h>
+
+int main(void) {
+  struct stat buf;
+
+  if(stat("/dev/sda", &buf) < 0){
+    printf("stat error for /dev/sda\n");
+    return -1;
+  }
+
+  printf("dev = %ld\nrdev = %ld\n", buf.st_dev, buf.st_rdev);
+
+  if(S_ISCHR(buf.st_mode)){
+    printf("character device\n");
+  }
+  else if (S_ISBLK(buf.st_mode)){
+    printf("block device\n");
+  }
+  else {
+    printf("unkonwn device\n");
+  }
+  
+  return 0;
+}