VMS Help CC, Run-time functions, printf, Optional character  *Conan The Librarian (sorry for the slow response - running on an old VAX)

  flags        You can use the following flag characters, alone or in
               any combined order, to modify the conversion
               specification:

               '         Requests that a numeric conversion is
                         formatted with the thousands separator
                         character.  Only the numbers to the left of
                         the radix character are formatted with the
                         separator character.  The character used as
                         a separator and the positioning of the
                         separators are defined in the program's
                         current locale.

               -(hyphen) Left-justifies the converted output source
                         in its field.

               +         Requests that an explicit sign be present on
                         a signed conversion.  If this flag is not
                         specified, the result of a signed conversion
                         begins with a sign only when a negative
                         value is converted.

               space     Prefixes a space to the result of a signed
                         conversion, if the first character of the
                         conversion is not a sign, or if the
                         conversion results in no characters.  If you
                         specify both the space and the + flag, the
                         space flag is ignored.

               #         Requests an alternate form conversion.
                         Depending on the conversion specified,
                         different actions will occur.  For the o
                         (octal) conversion, the precision is
                         increased to force the first digit to be a
                         0.  For the x (or X) conversion, a nonzero
                         result is prefixed with 0x (or 0X).  For e,
                         E, f, g, and G conversions, the result
                         contains a decimal point even at the end of
                         an integer value.  For g and G conversions,
                         trailing zeros are not trimmed.  For other
                         conversions, the effect of # is undefined.

               0         Uses zeros rather than spaces to pad the
                         field width for d, i, o, u, x, X, e, E, f,
                         g, and G conversions.  If both the 0 and the
                         - flags are specified, then the 0 flag is
                         ignored.  For d, i, o, u, x, and X
                         conversions, if a precision is specified,
                         the 0 flag is ignored.  For other
                         conversions, the behavior of the 0 flag is
                         undefined.

  field width  The minimum field width can be designated by a decimal
               integer constant, or by an output source.  To specify
               an output source, use an asterisk (*) or the sequence
               *n$, where n refers to the nth output source listed
               after the format specification.  If the converted
               output source is wider than the minimum field, write
               it out.  If the converted output source is narrower
               than the minimum width, pad it to make up the field
               width.  Pad with spaces, by default.  Pad with zeros
               if the 0 flag is specified; this does not mean that
               the width is an octal number.  Padding is on the left
               by default, and on the right if a minus sign is
               specified.

               If an asterisk is used for the field width, the
               corresponding width is given in the output source.

  period (.)   Separates the field width from the precision.

  precision    The precision defines the minimum number of digits to
               appear for d, i, o, u, x, and X conversions; the
               number of digits to appear after the decimal-point
               character for e, E, and f conversions; the maximum
               number of significant digits for g and G conversions;
               or the maximum number of characters to be written from
               a string in an s or S conversion.  If a precision
               appears with any other conversion specifier, the
               behavior is undefined.

               Precision can be designated by a decimal integer
               constant, or by an output source.  To specify an
               output source, use an asterisk (*) or the sequence
               *n$, where n refers to the nth output source listed
               after the format specification.

               If only the period is specified, the precision is
               taken as 0.

  h, l, or L   An h specifies that a following d, i, o, u, x, or X
               conversion specifier applies to a short int or
               unsigned short int argument; an h can also specify
               that a following n conversion specifier applies to a
               pointer to a short int argument.

               An l (lowercase ell) specifies that a following d, i,
               o, u, x, or X conversion specifier applies to a long
               int or unsigned long int argument; an l can also
               specify that a following n conversion specifier
               applies to a pointer to a long int argument.

               An L specifies that a following e, E, f, g, or G
               conversion specifier applies to a long double
               argument.

               If an h, l, or L appears with any other conversion
               specifier, the behavior is undefined.

               On Compaq C for OpenVMS VAX and Alpha Systems, int
               values are equivalent to long values.