how can I fix the MSVC 2005 error: unresolved external symbol __environ

Question

Hi,

In my application, I need direct access to the _environ variable because I must have something like the glibc unsetenv (you cannot have that with setenv or putenv).

This is the code I need to use:

//////////////////////
// unsetenv for WIN32, taken from libc source
int unsetenv(const char *name)
{
  size_t len;
  char **ep;

  if (name == NULL || *name == '\0' || strchr (name, '=') != NULL)
    {
      return -1;
    }

  len = strlen (name);

  ep = _environ;
  while (*ep != NULL)
    if (!strncmp (*ep, name, len) && (*ep)[len] == '=')
      {
    /* Found it.  Remove this pointer by moving later ones back.  */
    char **dp = ep;

    do
      dp[0] = dp[1];
    while (*dp++);
    /* Continue the loop in case NAME appears again.  */
      }
    else
      ++ep;

  return 0;
}

It has worked fine until we got some problems with manifests on some systems, so we tried to use the static version of the runtime library (/MT flag).

Now, I am getting this error:

unresolved external symbol __environ

I read here and at many other places that this variable has become obsolete and deprecated. I wonder about the possible solution. I also cannot use the _wenviron variable because we want to support Windows 98.

In the project settings, I explicitely set it to use MBCS (i.e., not Unicode). I am a bit stumbled here. Is there anything else I must set?

Just for testing, I also tried the Unicode version. I.e. this code:

int unsetenv(const wchar_t *name)
{
  size_t len;
  wchar_t **ep;

  if (name == NULL || *name == '\0' || wcschr (name, '=') != NULL)
    {
      return -1;
    }

  len = wcslen (name);

  ep = _wenviron;
  while (*ep != NULL)
    if (!wcsncmp (*ep, name, len) && (*ep)[len] == '=')
      {
    /* Found it.  Remove this pointer by moving later ones back.  */
    wchar_t **dp = ep;

    do
      dp[0] = dp[1];
    while (*dp++);
    /* Continue the loop in case NAME appears again.  */
      }
    else
      ++ep;

  return 0;
}

I wonder a bit why that even compiled because I explicitly have set it to use MBCS and not Unicode. But maybe that means something else. (Can somebody enlighten me here?)

Anyway, this results in these errors:

1>AuxLib.obj : error LNK2001: unresolved external symbol __wenviron
1>ExtractInfo.obj : error LNK2001: unresolved external symbol __environ

AuxLib.obj is the file with this unsetenv(). So one error more than before.

Answer 1

I'm not sure I understand, what's wrong with getenv_s()? It is the function equivalent of the global variable __environ. It is multibyte, not unicode, so it should work fine on all platforms targetted by the VS 2005 compiler. the "_s" means "safe", meaning the operation was re-designed to reduce exploitability by hackers via buffer overflows, etc.