string.Format() parameters

Question

How many parameters can you pass to a string.Format() method?

There must be some sort of theoretical or enforced limit on it. Is it based on the limits of the params[] type or the memory usage of the app that is using it or something else entirely?

Answer 1

OK, I emerge from hiding... I used the following program to verify what was going on and while Marc pointed out that a string like this "{0}{1}{2}...{2147483647}" would succeed the memory limit of 2 GiB before the argument list, my findings did't match yours. Thus the hard limit, of the number of parameters you can put in a string.Format method call has to be 107713904.

int i = 0;
long sum = 0;
while (sum < int.MaxValue)
{
    var s = sizeof(char) * ("{" + i + "}").Length;
    sum += s; // pseudo append
    ++i;
}
Console.WriteLine(i);
Console.ReadLine();

Love the discussion people!

Answer 2

Not as far as I know...

well, the theoretical limit would be the int32 limit for the array, but you'd hit the string length limit long before that, I guess...

Just don't go mad with it ;-p It may be better to write lots of small fragments to (for example) a file or response, than one huge hit.

edit - it looked like there was a limit in the IL (0xf4240), but apparently this isn't quite as it appears; I can make it get quite large (2^24) before I simply run out of system memory...

---

Update; it seems to me that the bounding point is the format string... those {1000001}{1000002} add up... a quick bit of math (below) shows that the maximum useful number of arguments we can use is 206,449,129:

    long remaining = 2147483647;// max theoretical format arg length
    long count = 10; // i.e. {0}-{9}
    long len = 1;
    int total = 0;
    while (remaining >= 0) {
        for(int i = 0 ; i < count && remaining >= 0; i++) {
            total++;
            remaining -= len + 2; // allow for {}
        }
        count *= 10;
        len++;
    }

    Console.WriteLine(total - 1);