h_errno - error return value for network database operations
endhostent(). Note that this method of returning errors is used only in connection with legacy functions.
<netdb.h>header provides a declaration of h_errno as a modifiable l-value of type int.
Applications should obtain the definition of h_errno by the inclusion of
<netdb.h>. The practice of defining h_errno in a program as an extern int h_errno is obsolescent.
It is unspecified whether h_errno is a macro or an identifier declared with external linkage. If a macro definition is suppressed in order to access an actual object, or a program defines an identifier with the name h_errno, the behaviour is undefined.
First released in Issue 4.