add C implementation of DFS example

07_trees/c/01_filesystem_dfs.c

@@ -0,0 +1,46 @@
+#include <dirent.h>
+#include <limits.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <sys/stat.h>
+
+int filter(const struct dirent *entry) {
+  return strcmp(entry->d_name, ".") != 0 && strcmp(entry->d_name, "..") != 0;
+}
+
+void printnames(const char *dir) {
+  struct dirent **entries;
+  int count = scandir(dir, &entries, filter, alphasort);
+
+  if (count < 0) {
+    perror("scandir");
+    return;
+  }
+
+  for (int i = 0; i < count; i++) {
+    char path[PATH_MAX];
+    snprintf(path, sizeof(path), "%s/%s", dir, entries[i]->d_name);
+
+    struct stat sb;
+    if (stat(path, &sb)) {
+      perror("stat");
+      free(entries[i]);
+      continue;
+    }
+
+    if (S_ISREG(sb.st_mode)) {
+      printf("%s\n", entries[i]->d_name);
+    } else if (S_ISDIR(sb.st_mode)) {
+      printnames(path);
+    }
+
+    free(entries[i]);
+  }
+  free(entries);
+}
+
+int main() {
+  printnames("pics");
+  return 0;
+}