About sprintf intercept decimal problem

Issue: Retain 1 decimal places, not rounded, 0 for integers

A lot of people say that sprintf('%.1f',$str); , but the results are still problematic.
Finally, this method is used to solve:echo sprintf('%.1f', floor($str));

Not to say no rounding? Why by rounding, 5 but not into, 6 only into;
And all the other functions are number_format($str) in the 5, which is why?

Reply content:

Issue: Retain 1 decimal places, not rounded, 0 for integers

A lot of people say that sprintf('%.1f',$str); , but the results are still problematic.
Finally, this method is used to solve:echo sprintf('%.1f', floor($str));

Not to say no rounding? Why by rounding, 5 but not into, 6 only into;
And all the other functions are number_format($str) in the 5, which is why?

I measured it, and visual inspection is the problem of the accuracy of floating point

Reference

Linux floating-point number rounding or five-six (floating-point representation)

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