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output string formatting

Posted on 1998-09-09
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Last Modified: 2010-04-10
Hi, in C one uses " %4.3lf " to string format a long double floating point value. And " %4.3f " for ordinary floating point values.

What is its  equivalent in C++ ? (i.e. for long double string formating)

I tried using setprecision(4), but this messes up the output which returns with a string of # signs and some alphanumeric characters.

setprecision() is meant for normal/ordinary floating point values, but I don't know which is the equivalent parameter for long double floating point values .

Thanks

Paul
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Question by:pdorai
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WxW earned 30 total points
ID: 1172316
The same . Functions included in stdio.h as printf are available to C++ . Furthermore , if your app is a windows app , use sprintf to create a buffer to format the text
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by:nietod
ID: 1172317
WxW, I think pdorai is trying to use streams.  Thus, the converting back to the C way is not a good idea.

setprecision(4) is not 100% equiviliant to C's %4.3f.  the precision is used in two ways.  If the stream is in automatic format or scientific format, then it will display 4 significant digits.  If the stream is in fixed format it will display 4 decimal digits.  You may need to set the width prior to ouputing the number to get the desired result.  
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by:snoegler
ID: 1172318
In my opinion is every C function also a C++ function - but i think that's bad karma, right?
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LVL 22

Expert Comment

by:nietod
ID: 1172319
Yes, but in many cases C++ provides improved ways to perform tasks that are not available in C.  C++'s I/O streams are an example.  They are more powerful and are much safer to use.  
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by:WxW
ID: 1172320
C++ streams are more powerful than printf and sprintf ?
For creating simple buffers ... I think that they are better & easier
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by:Paullkha
ID: 1172321
Here's a couple of ways!

CString text; //string???
float value = 1.30;
text.Format("$%7.2f", value);
(I like the above because you can easily see the formatting AND you are not changing the setup for cout)
or

cout.precision(4);
cout << 1.3456;

or

ios_base::fixed

etc...


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Expert Comment

by:Paullkha
ID: 1172322
#include <iostream>
#include <iomanip>
using namespace std;

int main()
{
      long double x;
      x = 12.3456;
      cout << setprecision(2) << fixed << setw(5) << x <<endl;
      return (0);
}
Is this what you want?
fixed is fixed decimal point
setprecision, as mentioned above, sets number of digits AFTER decimal point
setw sets the width to 5, this width INCLUDES the decimal point
Good luck
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