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POLimiting a floating point ostream print to a certain length?
 

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  1. POLimiting a floating point ostream print to a certain length?
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    <p>Here's a <a href="https://stackoverflow.com/questions/554063/how-do-i-print-a-double-value-with-full-precision-using-cout">related topic</a>. </p> <p>I'm looking for something slightly different, I'm printing out a 4x4 floating point matrix. In fact I'm using <a href="https://stackoverflow.com/questions/4850473/pretty-print-c-stl-containers">this prettyprint method</a> to do it, which will preclude me from using <code>printf</code> formatting which I'm a little more familiar with. </p> <p>I can set <code>ios_base::width()</code> to set a minimum width to pad out the zeros and ones but the likes of <code>0.6666667</code> screws up the alignment. I figure I can set <code>precision</code> but it only affects the number of significant figures and not the total number of char's produced by the value. I can't seem to use <code>unsetf</code> on an <code>ostream</code> to set 'default notation'... Even if I could do that I suspect a minus sign would mess up alignment anyway. </p> <p>Is there a workaround? </p>
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    1. USSteven Lu
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    1. COWhat do you intend to do if you limit yourself (e.g.) to 4 characters and someone wants to use (e.g.) 55432(.123456)? It may be ok to lose precision, which buys you space after the decimal point, but not before. Maybe you could work out the widest you need, then pad the others out to that?
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      1. POLimiting a floating point ostream print to a certain length?
      1. USBoBTFish
    2. COIdeally I'd just like to print out the left-most n characters: n=4: 0.004 or 243.2 or -222. if I have a value bigger or smaller than can be expressed this way, then I don't need to know what the exact value is. It seems like I may need to do some custom string handling to get the exact behavior i'd want... I was able to get `setf(std::ios_base::fixed)` to work which is better than before but I do have the minus sign issue, and like you said, it doesnt count digits coming before the decimal point. Am I to assume there is no mechanism for me to limit width? But it's possible with `printf`...
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      1. POLimiting a floating point ostream print to a certain length?
      1. USSteven Lu
    3. COI'm looking at `std::setprecision` from `<iomanip>` now. Nope, it looks like that does nothing other than call `precision` more conveniently. I also seem to be wrong about `printf` being able to do this, too. It doesn't allow me to truncate! So the minus sign goes along with the other preceding digits as something I have to deal with on my own. Somebody please make an answer to give a solution (other than the straightforward `sprintf` hackery) or to verify that there is no stdlib solution as I suspect now.
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      1. USSteven Lu
 

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