Re: [Mingw-users] Building GNU-Global: setenv() is missing

[Keith M. <kei...@to...>]

Daniel K. O. wrote:
> Even though the mysetenv() code seems to
> leak memory, that's necessary for putenv() - it doesn't copy the
> argument, it just points to it; so if you change (or free) the
> string after the putenv() call, you may mess with the environment.

`seems' is very much the operative word here, for the mysetenv
example does *not* leak memory, *if* the putenv call is successful.
Yes, the pointer to the string eventually passed to putenv is
not directly exposed beyond the scope of mysetenv; it is a local
pointer to a malloc'ed buffer, so the buffer continues to exist
after mysetenv returns, but the pointer is lost; however, it may
be retrieved subsequently, by calling getenv.

BTW, I didn't write that sample function; it is exactly as it was
in the man-1.5m sources I ported, and may very well be John Eaton's
original code.  I guess it could be made more robust by free'ing
the buffer before returning, if the putenv call fails:

  static void
  mysetenv(const char *name, const char *value) {
  #ifdef HAVE_SETENV
    setenv(name, value, 1);
  #else
    int len = strlen(value)+1+strlen(value)+1;
    char *str = my_malloc(len);
    sprintf(str, "%s=%s", name, value);
    if(putenv(str) != EXIT_SUCCESS)
      free(str);
  #endif
  }

(The my_malloc function is a wrapper around malloc; it aborts the
 program, with an `Out of memory' message, if malloc itself fails).

Regards,
Keith.