C-style formatting

[fortran-lang]

C-style formatting

[marshallward]

Python 3 formatting is becoming quite widespread; I know that C# and Rust use them. It would be great to reach this point, but I agree with @cmacmackin that it might not be practical with Fortran syntax.

Those languages also offer C-style formatting, so I see no harm in pursuing both.

[longb]

Note that the Fortran 202X proposal list includes intrinsic functions for converting Fortran characters to C strings and vice versa.

[certik]

Perhaps using the Python 3 formatting syntax would work for Fortran: https://docs.python.org/3.1/library/string.html#format-specification-mini-language (see examples).

[cmacmackin]

A bit more thought makes me wonder if it would in fact be better to do this in Fortran, as converting between Fortran and C strings is quite a painful really.

Furthermore, some of the behaviour of printf is not exactly idiomatic for Fortran. In particular, Fortran does not have the concept of \t, \n, etc. within strings. Also, printing in Fortran would normally result in a new-line after, while this is not the default behaviour for printf (although it would be very easy to add a new-line). As such, it might be worth considering whether we want to define formatted printing that is specific to Fortran, perhaps using a syntax more like Python's format strings.

[14NGiestas]

I agree with @gronki and I think this whole issue should migrate to a "string style formatting" type of discussion (For instance: #69 ) closing this one. We could implement some facility to convert a easier to write and read syntax to the standard way.
For example, take some sane string:

"My name is (A) and I want a readable spec, so I can show pi = (G0) and fruits = (I0) to my friends."

and convert to the weird and sometimes infuriating standard I/O

'("My name is ",A," and I want a readable spec, so I can show pi = ",G0," and fruits = ",I0," to my friends.")'

Then, finally using it as a sane format

write(f, sane_fmt) 'Ian', PI, my_fruits

Such facility would fit into a string module (like Python did, actually).

IDK, what you all think @certik @gronki @cmacmackin ?
PS: Related J3 proposal by gronki #69

[certik]

We can start with using C, and later we can perhaps reimplement in Fortran if we decide it is valuable to stay in pure Fortran (see #20).

[cmacmackin]

@certik Yes, that's what I was thinking of, although I don't think it would be practical to allow named-arguments in the format string, given Fortran doesn't have features like that.

[certik]

We can start without named arguments. Then go from there, perhaps there is a way to specify the names somehow, that is quite reasonable syntax-wise.

[gronki]

I agree C-style formatting is already considered obsolete in Python. I would prefer just improving the currect capabilities of Fortran i/o.

On a side note, there has been recently a whole discussion whether "things easy to implement should be implemented or left for the programmer". My stand on this is "they should be implemented if they are the recommended way of doing things". Using C stdlib in Fortran is certainly not the purest way of doing things (and might possibly bring portability issues) so I would leave this burden and responsibility to the programmer.

What do you think?