Printing particularities of pgf77 (FORTRAN 77 behaviour?) - formatting

Question

I compile and run this simple FORTRAN 77 program:
program test
write(6,*) '- - - - - - - - - - - - - - - - - - - - - - - - - - ',
& '- - - - - - - - - - - - - - - - - - - - - - - - - -'
write(6,'(2G15.5)') 0.1,0.0
end
with gfortran or f95 the output is:
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
0.10000 0.0000
with pgf77 it is:
- - - - - - - - - - - - - - - - - - - - - - - - - -
- - - - - - - - - - - - - - - - - - - - - - - - - -
0.10000 0.00000E+00
and with g77 or ifort:
- - - - - - - - - - - - - - - - - - - - - - - - - -
- - - - - - - - - - - - - - - - - - - - - - - - - -
0.10000 0.0000
A couple of questions arise:
Why is 0.0 printed with four decimal places instead of five, as
requested in the format G15.5? Is this spec-compliant? And why
does pgf77 write it differently?
I guess the line break in the - - - - - - line with the last three
compilers is due to some limitation in the output line length... Is
there any way of increasing this limit, or otherwise force
single-line writes, at compile time?
By the way, the desired output is
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
0.10000 0.00000
which matches none of the above.

Answer 1

Exactly what the G edit descriptor causes to be printed is a little complicated but for the value 0.0 the standard (10.7.5.2.2 in the 2008 edition) states that the compiler should print a representation with d-1 (ie 4 in your example) digits in the fractional part of the number. So most of your compilers are behaving correctly; I think that pgf77 is incorrect but it may be working to an earlier standard with a different requirement.
The simplest fix for this is probably to use an f edit descriptor instead, (2F15.5).
As for the printing of the lines of hyphens, your use of the * edit descriptor, which causes list-directed output, surrenders precise control of the output to the compiler. My opinion is that it is a little perverse of a compiler to print the two parts of the expression on two lines but it is not non-standard behaviour.
If you want the hyphens printed all on one line take control of the output format, write(6,'(2A24)') or something similar ought to do it (I didn't count the hyphens for you, just guessed that there are 24 in each part of the output.) If that doesn't appeal to you simply write one string with all the hyphens in; that will probably get written on one line even using list-directed output.