What is the equivalent of /proc/self/exe on Macintosh OS X Mavericks?

I'm porting a Linux C++03 application to Darwin OS X and have some code that reads the symbolic link at /proc/self/exe to determine the directory in which the executable running is located.

How can I compute the directory of the current executable running on Macintosh Darwin OS X Mavericks in C++?

Here is my existing code that works on Linux:

bool
resolveBinaryLocation(string &binaryDirname)
{
  // Read the symbolic link '/proc/self/exe'.
  const char *linkName = "/proc/self/exe";
  const size_t bufSize = PATH_MAX + 1;
  char dirNameBuffer[bufSize];
  const int ret = int(readlink(linkName, dirNameBuffer, bufSize - 1));

  if (ret == -1) {
    // Permission denied (We must be inetd with this app run as other than root).
    return false;
  }

  dirNameBuffer[ret] = 0; // Terminate the string with a NULL character.

  binaryDirname = dirNameBuffer;

  // Erase the name of the executable:
  string::size_type last = binaryDirname.size() - 1;
  string::size_type idx  = binaryDirname.rfind(DSI_PATH_CHAR, last);

  // Add one to keep the trailing directory separator.
  binaryDirname.erase(idx + 1);

  return true;
}

Here is what I settled upon as a solution:

bool
resolveBinaryLocation(string &binaryDirname)
{
  const size_t bufSize = PATH_MAX + 1;
  char dirNameBuffer[bufSize];

#ifdef __APPLE__
  uint32_t size = bufSize;

  if (_NSGetExecutablePath(dirNameBuffer, &size) != 0) {
    // Buffer size is too small.
    return false;
  }
#else // not __APPLE__
  // Read the symbolic link '/proc/self/exe'.
  const char *linkName = "/proc/self/exe";
  const int ret = int(readlink(linkName, dirNameBuffer, bufSize - 1));

  if (ret == -1) {
    // Permission denied (We must be inetd with this app run as other than root).
    return false;
  }
    
  dirNameBuffer[ret] = 0; // Terminate the string with a NULL character.
#endif // else not __APPLE__

  binaryDirname = dirNameBuffer;

  // Erase the name of the executable:
  string::size_type last = binaryDirname.size() - 1;
  string::size_type idx  = binaryDirname.rfind(DSI_PATH_CHAR, last);

  // Add one to keep the trailing directory separator.
  binaryDirname.erase(idx + 1);

  return true;
}