5.4 Reading & Displaying Dates with Informats and Formats

5.4 Reading & Displaying Dates with Informats and Formats

Quick Answer: The content guide's date objective has three parts: explain how SAS stores dates, use SAS informats to read common date and time expressions, and use SAS date and time formats to specify how the values are displayed. An informat is an input instruction (MMDDYY10.); a format is an output instruction (DATE9.). Both matter because the stored value is only a count of days since 1 January 1960.

---

1. Informat or Format? The One-Line Test

Reading "31OCT2026" with DATE9. and displaying 24775 with DATE9. are different operations that happen to share a name. SAS resolves the ambiguity by position: whatever follows a variable in an INPUT statement is an informat, whatever follows it in a FORMAT statement is a format.

---

2. Informats That Read Common Date Expressions

data work.read_dates;
   infile datalines truncover;
   input @1  us_date  mmddyy10.
         @12 iso_date yymmdd10.
         @23 sas_date date9.
         @33 clock    time8.;
   format us_date iso_date sas_date date9. clock time8.;
   datalines;
10/31/2026 2026-10-31 31OCT2026 14:30:00
;
run;

All four raw strings become numbers. us_date, iso_date, and sas_date all hold 24775; clock holds 52200.

The INPUT Function Does the Same Job in Memory

data work.convert_dates;
   set work.raw_strings;                       /* HireText is character */
   HireDate = input(HireText, mmddyy10.);      /* numeric SAS date      */
   format HireDate date9.;                     /* without this it prints 24775 */
run;

Exam Trap: a variable created by INPUT() has no format attached. It is a perfectly correct SAS date value that prints as a bare integer until a FORMAT statement is applied. A question showing 24775 where the candidate expected 31OCT2026 is testing exactly this distinction.

---

3. Informat Width Rules

The w in MMDDYYw. is the number of raw characters to read, not the number of digits in the year.

A too-narrow informat rarely raises an error. It quietly produces a wrong date, which is the textbook definition of a logic error.

Two-Digit Years and YEARCUTOFF=

When an informat receives a two-digit year, the YEARCUTOFF= system option supplies the century. It sets the first year of a rolling 100-year window and defaults to 1926 in SAS 9.4, so the window runs 1926 through 2025.

options yearcutoff=1926;      /* the SAS 9.4 default: window = 1926-2025 */

data work.century;
   d1 = input('10/31/26', mmddyy8.);   /* 31OCT1926 */
   d2 = input('10/31/40', mmddyy8.);   /* 31OCT1940 */
   d3 = input('10/31/20', mmddyy8.);   /* 31OCT2020 */
   format d1 d2 d3 date9.;
run;

Within the 1926-2025 window, two-digit years 26 through 99 map to 1926-1999 and 00 through 25 map to 2000-2025. A file that records the year 2026 as 26 therefore imports as 1926 unless you raise the cutoff:

options yearcutoff=1950;    /* window becomes 1950-2049 */
data _null_;
   d = input('10/31/26', mmddyy8.);   /* now 31OCT2026 */
   put d = date9.;
run;

The dependable defence is to demand four-digit years in every source file rather than reasoning about the window at all.

---

4. Formats That Display Date Values

data work.display_variants;
   d      = '31OCT2026'd;
   run_dt = '31OCT2026:14:30:00'dt;
   format d date9. run_dt datetime20.;
run;

proc print data=work.display_variants;
   format d worddate18.;     /* overrides the permanent format for this step only */
run;

A FORMAT statement inside a DATA step attaches the format permanently; inside a PROC step it applies for that step alone. Because formats never alter the stored number, arithmetic, sorting, INTCK, and INTNX continue to operate on the underlying day count no matter how the value is displayed.

Exam Tip: the width of a format must be wide enough for the result. DATE7. applied to 31OCT2026 prints 31OCT26, and a badly undersized format prints asterisks. When output shows unexpected ***, suspect the format width first.