<stdlib.h>
getenv
char *getenv(const char *name);
The function searches an environment list, which each implementation defines, for an entry whose name matches the string name. If the function finds a match, it returns a pointer to a static-duration object that holds the definition associated with the target environment name. Otherwise, it returns a null pointer. Do not alter the value stored in the object. If you call getenv again, the value stored in the object can change. No target environment names are required of all environments.
 

/*--------------------------------------------------------------------------*

Name getenv, _wgetenv - get string from environment

Usage char *getenv(const char *envvar);
whar_t *_wgetenv(const wchar_t *envvar);

Prototype in stdlib.h

Description The environment consists of a series of entries that
are of the form:

name=string\0

The global variable environ points to an array of pointers
to these entries. The last pointer in the array is NULL.
getenv searches the environment for the entry corresponding
to envvar, then returns a pointer to string.

The string comparison is NOT case-sensitive.

Return value On success, getenv and _wgetenv return a pointer to the value
associated with envvar.

*---------------------------------------------------------------------------*/

_TCHAR * _RTLENTRY _EXPFUNC _tgetenv_nolock(const _TCHAR *nameP)
{
#if defined(_UNICODE)
if (_ostype & _WINNT)
{
#endif
_TCHAR **envP;
int len;

len = _tcslen(nameP); /* save length of name */
if (len == 0)
return NULL;

for (envP = _tenviron; *envP != NULL; envP++)
if (_tcsnicmp(*envP,nameP,len) == 0 && (*envP)[len] == _TEXT('='))
break;

if (*envP)
return ((*envP)+len+1); /* point past the '=' */
else
return (NULL);
#if defined(_UNICODE)
}
else
return NULL;
#endif
}