Unlike many Fortran implementations, FTN95 preprocesses 'constant' formats at compile-time. These 'constant' formats are as follows:
A FORMAT statement.
A format expression that is a character constant or a character constant expression.
A format expression that is a parameter name.
All formats which include character arrays, array elements or variables are decoded at run-time. Such non-constant formats require more extensive decoding which leads to longer execution times.
For example, the following should be avoided wherever possible:
F = '(3F10.4)'
. . .
It could be rewritten as follows:
. . .
so that the format specifier would be decoded at compile-time.
Note also that the colon (:) edit descriptor and tab facilities can often be used instead of a run-time format.