# How to use str2double without rounding

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Aditya Deshmukh 2017 年 1 月 20 日

Hi , I know this could be a possible duplicate but all those solutions stated there didn't work for me. I am using the str2double function and it always rounds the conversion to the 4 places after the decimal point. Do you guys have any idea on converting the whole string exactly the way it is without rounding ??
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Adam 2017 年 1 月 20 日

It doesn't do this for me at all.
>> str2double( '4.34576543' )
ans =
4.34576543
It seems to round to the 14th decimal place when I try it:
>> str2double( '4.34576543197566529101' )
ans =
4.34576543197567

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### 採用された回答

Nut 2017 年 1 月 20 日
Hi,
maybe you need a proper set of the output display format:
https://it.mathworks.com/help/matlab/ref/format.html
The default format is "short", with the "long" format you can see more digits, look at the following example.
A = '0.219033048405430510873439814';
>> A
A =
0.219033048405430510873439814
>> str2double(A)
ans =
0.2190
>> format long
>> str2double(A)
ans =
0.219033048405431

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### その他の回答 (1 件)

Stephen23 2017 年 1 月 20 日

str2double does not do any rounding: does its documentation mention "rounding" anywhere? In fact you are just getting confused by how numbers as displayed in MATLAB. How number values are displayed is a totally different thing to how they are stored in memory. str2double reads all of those digits correctly.
Use format to change how numbers are displayed:
>> format shortg
>> str2double('0.1234567890123456789')
ans = 0.12346
>> format longg
>> str2double('0.1234567890123456789')
ans = 0.123456789012346
There are plenty of format options: read the documentation and try some. Note that the double type is limited as to how many digits of precision it can handle. This is also not str2double's fault.

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