setprecision() - can I count on it rounding or not?

This is a discussion on setprecision() - can I count on it rounding or not? within the C++ Programming forums, part of the General Programming Boards category; okay, so here's the story: Back in my high school programming classes, we were told that iomanip didn't round. In ...

  1. #1
    Registered User major_small's Avatar
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    setprecision() - can I count on it rounding or not?

    okay, so here's the story: Back in my high school programming classes, we were told that iomanip didn't round. In my college classes, whenever we needed to round, we did it on our own.

    Then somebody on these boards told me it did round, so I took a closer look at it and found out that it did round. Then in an IRC channel, somebody asked if it rounded, and somebody replied saying that it was locale specific, and not to rely on it rounding.

    I tried checking the standard, and couldn't make any real sense out of what they said about it, and all of the explanations I could find about setprecision said something along the lines of "Sets the number of digits of precision".

    so my question is this: Can I depend on setprecision to round numbers all the time?
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    hi ....

    can you try this link:

    http://www.cplusplus.com/ref/iostrea...precision.html

    cio

  3. #3
    Registered User major_small's Avatar
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    ...I read that already... all it says is:
    The precision determines the maximum number of digits that shall be output on insertion operations to express floating-point values, counting both the digits before and after the decimal point.
    but that doesn't say anything about rouding at all... they show you in their example that it rounds, but that's the only place, and it's shady at that.

    edit: the answer may lie in the definition of the word precision itself...

    Quote Originally Posted by The American HeritageŽ Dictionary of the English Language, Fourth Edition
    The number of significant digits to which a value has been reliably measured.
    Quote Originally Posted by wiktionary
    (mathematics) the number of significant digits to which a value may be measured reliably
    but then I guess that kinda leaves it up to interpretation... but I'm still wondering if I'm missing anything in the standard that says it should round a number...
    Last edited by major_small; 11-23-2005 at 02:52 PM.
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