多次调用时 fwrite() 会覆盖吗？

Question

Example: I am going through a tree and fwriting based on preorder traversal.

This is pseudocode:

void func x ('','')
{
  do something 
  helper (char * filename, thing to be written);
}

void helper (char * filename, thing to be written)
{
  FILE * fp = fopen (filename,"w");
  fwrite(, , ,fp);
  fclose(fp);
  return 0;
}

Would it overwrite previous entries? If so, how can I prevent this? Is there a better way to do this?

Answer 1

As kaylum mentioned, the short answer is yes it does.

fopen with "w" will open the file at the beginning, so any writes will truncate and overwrite. In order to avoid this, either reuse the file pointer returned by fopen every time, or use "a" in order to set fwrite to append mode.