#define _TIMESPEC_DEFINED struct timespec { time_t tv_sec; long tv_nsec; };

The given code snippet defines a structure in the C programming language called "timespec" using the preprocessor directive #define.

Step 1: Preprocessor Directive

The preprocessor directive #define is used to define a macro in C. In this case, the macro being defined is _TIMESPEC_DEFINED. The macro is a symbolic name that can be used to represent a value or a block of code. It is used to ensure that the structure definition is not repeated if the code is included multiple times.

Step 2: Structure Definition

The structure definition begins with the keyword struct followed by the name of the structure, which is timespec. The structure contains two members: tv_sec of type time_t and tv_nsec of type long.

Step 3: Member Variables

The member variables tv_sec and tv_nsec represent the seconds and nanoseconds of a time value, respectively. The time_t type is used to represent time in seconds, while long is a data type that can hold a larger range of integer values.

By defining this structure, the code provides a way to store and manipulate time values with precision up to nanoseconds.