Re: Use fprintf in UEFI

[GN Keshava <keshava.gn@gmail.com>]

Thank you for detailed answer. Laszlo.

Regards,
Keshava

On Thu, 29 Sep 2016 at 13:01 Laszlo Ersek <lersek@redhat.com> wrote:

> CC Jaben
>
> On 09/29/16 08:01, GN Keshava wrote:
> > Hi,
> >
> > There is fprintf function in Stdio library. But how to use it? The first
> > argument is "FILE" type. But I have "EFI_FILE_PROTOCOL* File" which I got
> > from "EFIOpenFile" function. How to map to "FILE" type?
> >
> > Sorry if this is silly. A newbie here. Didn't get much idea in internet
> > search. :)
>
> (1) You're trying to mix edk2 APIs with standard C library APIs. Don't
> do that.
>
> I think what you are missing is the fact that using edk2, you can write
> a UEFI application *either* against edk2 APIs (protocols and libraries),
> *or* against standard C APIs (using the stdlib implementation of edk2).
> In some cases it is okay to call edk2 APIs directly, from stdlib
> applications, but in general I'd advise against that.
>
> I told you to read "AppPkg/ReadMe.txt"; that file explains what is
> necessary for what "flavor" of UEFI application. It even mentions two
> example programs, "Main" and "Hello", which don't do anything but
> highlight the differences.
>
> For another (quite self-contained) example,
> "AppPkg/Applications/OrderedCollectionTest" is an application that I
> wrote myself; it uses fopen() and fprintf(). This is a unit tester for
> an MdePkg library that I also wrote, so it actually exemplifies how you
> can use both stdlib and an edk2 library, as long as they don't step on
> each other's toes.
>
> (2) You can write formatted output to files using only edk2 APIs as
> well, but for that, you first have to format the text into memory
> buffers with PrintLib functions, then write the buffers to files with
> the ShellLib APIs or with direct protocol calls.
>
> (3) The standard C lib implementation in edk2 is only available for use
> by UEFI applications (no other module types; that is, no drivers).
> What's more, those applications have to be started from the shell (you
> can't boot them directly from the boot manager, for example). This is
> also documented in AppPkg/ReadMe.txt.
>
> Thanks
> Laszlo
>