An error indicator is returned by many GPHIGS functions, but mostly by the inquire functions. A program calls a GPHIGS function, passing a pointer to a variable to receive the error indicator. In the event that an error is detected, a value which indicates the nature of the error is returned by the GPHIGS function. When no error is detected a value of 0 is returned.
The values noted in the ERRORS section of each function description in the GPHIGS C Functions Manual, indicate which errors may occur when a particular function is called. Each value is noted with a brief description of the type of error or of the reason for the error. In C, The include file phigs.h defines the symbolic equivalents of these error values, which all have the prefix PE. It is recommended that these error symbols be used rather than the values themselves.