char *getenv(const char *name);

The default implementation returns NULL, indicating that no environment information is available.

If you re-implement getenv(), it is recommended that you re-implement it in such a way that it searches some form of environment list for the input string, name. The set of environment names and the method for altering the environment list are implementation-defined. getenv() does not depend on any other function, and no other function depends on getenv().

A function closely associated with getenv() is _getenv_init(). _getenv_init() is called during startup if it is defined, to enable a user re-implementation of getenv() to initialize itself.

The return value is a pointer to a string associated with the matched list member. The array pointed to must not be modified by the program, but might be overwritten by a subsequent call to getenv().