Getting number of digits in uint64_t

[raevin]

Long story short, my issue is that I'm having a hard time trying to get the number of digits in a uint64_t variable. The reason I'm using this is I want to make sure I get x amount of digits inside of a variable before I use it, but since the higher the digits, the better the program is.

I currently use the following code, and it works, but my loop will never exit because the length is always 0:

/**
 * numbdigits()
 * number:      The number to evaluate  [in]
 *
 * Returns the number of digits found in a number.
 **/
uint64_t numdigits(uint64_t number){
        uint64_t tmp = number;

        uint64_t i = 0;

        if(number < 0)
                tmp = -tmp;

        while(tmp){
                tmp /= 10;
                i++;
        }

        return i;
}

Here's my code with the loop (that calls numdigits()):

uint64_t sized_num(int digits){
        uint64_t val = 2;
        uint64_t tmp = 0;
        uint64_t curd = 0; // Current digits

        while(curd <= digits){
                tmp = getrand(1, 2, 3, 4, 5, 6);
                val = tmp * tmp;
                curd = numdigits(val);
        }

        return val;
}

Anyone know what's going on? :/ getrand() returns a uint64_t as well (and works). The only way the while() loop ends without my intervention is if I do curd += numdigits(val) instead...but, that gives a false value as well.

[Rubberman]

First, a uint64_t is unsigned. Your test for number < 0 is meaningless. Myself, I would consider printing the number to a string and then seeing what the length is. IE:

char buffer[256];
return sprintf(buffer, "%llu", number);

I have oversized the buffer length just to be "safe". You can reduce the size according to the maximum number of digits you can find in a 64-bit unsigned integer. Since sprintf() returns the number of digits printed, there you have the answer with a minimum of fuss.

[Bemk]

I generally tend to printf stuff in a standard format (especially in a loop, and then end the program so I can look at the output). It gives you more of an idea to how the data flows. Another option could be to use gdb. Just debug the thing, with a good debugger (such as gdb) or the poor mans debugger (printf(%X, val)