#include <stdlib.h>char *getenv(const char *name);
The getenv( ) function returns a pointer to environmental information associated with the string pointed to by name in the implementation-defined environmental information table. The information must not be changed by your code.
The environment of a program may include such things as path names and devices online. The exact nature of this data is implementation defined. You will need to refer to your compiler’s documentation for details.
If a call is made to getenv( ) with an argument that does not match any of the environment data, a null pointer is returned.
A related function is system( ).