How to print floating point value using putchar?

Question

I am working on an embedded application and need to print floating point values. Due to space and other limitations I can only use putchar() for output.

I am trying

Answer 1

What range of values and accuracy/precision requirements do you need? Printing the exact value of a floating point number in decimal is a very hard problem and requires up to 8 kb or so (I could be off by a few powers of 2; this is off the top of my head) of working space if you support 80-bit or 128-bit long double values. You can probably get by with 1 kb or so if you only support double, and essentially no working space if you just want to print poor approximations.

OK, so here's a really basic version:

void putDouble(double x, int p)
{
    long d;
    if (x<0) {
        putchar('-');
        x=-x;
    }
    d = x;
    putLong(d);
    putchar('.');
    while (p--) {
        x = (x - d) * 10;
        d = x;
        putchar('0'+d);
    }
}

You might want to fix your putLong to handle numbers longer than 2 digits, 2. :-)