Defining the Date and Time Data Type
Originally, the UNIX time and date value was stored in the C data type long. As time passed, and as standardization efforts got underway, it was recognized that this was not good for long-range planning. The capacity of the long integer was going to run out someday (January 19, 2038, at 03:14:07 UTC, to be precise). The next second after that will cause the 31-bit positive number to roll over to a 32-bit value, making it a negative number.
Since the long integer data type was going to overflow in the near future, it was decided that date and time deserved its own special data type: time_t. This permits the underlying data type to be changed at a future date, requiring that applications only be recompiled. ...
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