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Asked: 2026-05-19T03:23:37+00:00

I have problem on UNIX based systems sprintf does not round up properly value.

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I have problem on UNIX based systems sprintf does not round up properly value.

For example

double tmp = 88888888888885.875
char out[512];

Thats 88,888,888,888,885.875 just to be easier on eyes.
I am giving such specific and big example because it seems it works fine on smaller numbers.

I am trying to use it in following way

sprintf(out, "%021.2f", tmp);
printf("out = %s\n", tmp);

On windows this results in:

out = 000088888888888885.88

On for example AIX, but shows in Linux as well:

out = 000088888888888885.87

Why is this happening?
Any ideas and how to make it behave same way on Win/Unix

Thanks

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1 Answer

  1. Editorial Team

    There is a bug report for glibc with a problem very similar to yours. The main conclusion (in comment 46) here is that double is not a 15-decimal-digit number and you should not expect it to work like that.

    As a workaround you can add something small to your numbers to make them round better. But this solution is not general because it depends on number ranges you deal with.

    Another workaround can be multiplying to prepare them for rounding, then rounding (e.g. 2597.625*100 = 259762.5 -> 259763 = 2597.63*100)

    However I think there must be smarter workarounds.

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