c++ - Why would clang++ fail to compile on a Mac, under Mavericks, except with sudo?

After a most recent software update on my mac, I'm not able to compile and link a c++ hello world program without sudo.

The program (helloworld.cpp):

#include 

int main(){
  std::cout << "hello world\n";
  return 0;
}

The invocation:

clang++ helloworld.cpp

Fails with error:

ld: can't write output file: a.out for architecture x86_64
clang: error: linker command failed with exit code 1 (use -v to see invocation)

But if I do this under sudo,

sudo clang++ helloworld.cpp

There's no problem.

What might be causing this, and how might I be able to resolve this?

---

EDIT, again: The answer turned out not to be working directory permissions, as a couple of people suggested, but the permissions associated with the output file, a.out, of my hello world program. Credit to Petesh for the solution.

Answer

You must be sitting in a directory which is not writable by your user. Look at pwd and ls -ld . to see where you are and what the permissions are there. Try also creating an empty file by touch foo.txt in the same directory where you ran Clang.