PIC C18: Converting double to string

Question

I am using PIC18F2550. Programming it with C18 language.
I need a function that converts double to string like below:

void dtoa(  char *szString,             // Output string
            double dbDouble,            // Input number
            unsigned char ucFPlaces)    // Number of digits in the resulting fractional part
{
    // ??????????????
}

To be called like this in the main program:

void main (void)
{
    // ...
    double dbNumber = 123.45678;
    char szText[9];
    dtoa(szText, dbNumber, 3); // szText becomes "123.456" or rounded to "123.457"
    // ...
}

sprintf() then find the '.' and null the right decimal character? — kenny
– kenny, Commented Feb 7, 2012 at 21:44
@MartinBeckett I'm sure it's available if you have the space. Or roll your own dtoa() — kenny
– kenny, Commented Feb 7, 2012 at 21:52
"Available" can be a nuanced question since standards like MISRA ban the use of variable arguments... — Throwback1986
– Throwback1986, Commented Feb 7, 2012 at 22:02
I use sprintf all the time on the PIC18, and doubles as well. — Adam Casey
– Adam Casey, Commented Apr 5, 2012 at 15:41

Martin Beckett · Accepted Answer · 2012-02-07 21:47:02Z

1

So write one!

5mins, a bit of graph paper and a coffee is all it should take.
In fact it's a good interview question

answered Feb 7, 2012 at 21:47

Martin Beckett

96.3k28 gold badges196 silver badges268 bronze badges

Sign up to request clarification or add additional context in comments.

Comments

Brooks Moses · Accepted Answer · 2012-02-07 22:35:52Z

Generally, the Newlib C library (BSD license, from RedHat, part of Cygwin as well as used in many many "bare-metal" embedded-systems compilers) is a good place to start for usefuls sources for things that would be in the standard C library.

The Newlib dtoa.c sources are in the src/newlib/libc/stdlib subdirectory of the source tree:

Online source browser: http://sourceware.org/cgi-bin/cvsweb.cgi/src/newlib/libc/stdlib/?cvsroot=src#dirlist
Direct link to the current version of the dtoa.c file: http://sourceware.org/cgi-bin/cvsweb.cgi/~checkout~/src/newlib/libc/stdlib/dtoa.c?rev=1.5&content-type=text/plain&cvsroot=src

The file is going to be a little odd, in that Newlib uses some odd macros for the function declarations, but should be straightforward to adapt -- and, being BSD-licensed, you can pretty much do whatever you want with it if you keep the copyright notice on it.

Throwback1986 · Accepted Answer · 2012-02-07 21:51:00Z

0

Tiny printf might work for you: http://www.sparetimelabs.com/tinyprintf/index.html

answered Feb 7, 2012 at 21:51

Throwback1986

5,9951 gold badge35 silver badges23 bronze badges

2 Comments

Michael Burr Over a year ago

As mentioned on that page: "Of course being tiny, it has limitations, no floating point support..."

Throwback1986 Over a year ago

Ah yes, good catch. Now I dimly recall rolling in our own floating point.

Collectives™ on Stack Overflow

PIC C18: Converting double to string

3 Answers 3

Comments

Comments

2 Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

3 Answers 3

Comments

Comments

2 Comments

Your Answer

Sign up or log in

Post as a guest

Related