When using fprintf to format multiple strings, what does the integer after the % sign do?

Question

Matthew Cooper 2013-1-29

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https://ww2.mathworks.cn/matlabcentral/answers/60275-when-using-fprintf-to-format-multiple-strings-what-does-the-integer-after-the-sign-do

Hi,

Given something such as:

fprintf('%5d %10.3f %8.5e\n',100,2*pi,pi);

What do the numbers directly after the % sign do? I understand that %5d displays an integer, 5 spaces in from the beginning of the line. But, I don't understand what the %10 does. I know the .3f says to display decimal format with 3 decimal places, but what does the 10 do? And what does the %8 do? If I type

fprintf('%5d %3.3f %8.5e\n',100,2*pi,pi); or fprintf('%5d %4.3f %8.5e\n',100,2*pi,pi);

I get the same answer. It isn't until I get to

fprintf('%5d %6.3f %8.5e\n',100,2*pi,pi);

That the spacing changes, and then the spacing increases by 1. So, I see that it seems to be related to the previous spacing argument, but I can't figure out the exact pattern. Clarification would be greatly appreciated. Thank you!

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Answer 1

Shashank Prasanna 2013-1-29

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https://ww2.mathworks.cn/matlabcentral/answers/60275-when-using-fprintf-to-format-multiple-strings-what-does-the-integer-after-the-sign-do#answer_72820

It is the field width or the minimum numbers of characters to print.

Check this link out:

http://www.mathworks.com/help/matlab/ref/fprintf.html#inputarg_formatSpec

scroll down for a diagrammatic representation and explanation.

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Matthew Cooper 2013-1-30

编辑：Matthew Cooper 2013-1-30

Thank you for the link, but I don't think it's as simple as saying that it is the field width or the minimum numbers of characters to print. If you notice in the example I provided, the second argument seems to depend on the first argument, e.g. %10.2f, %5.3d will produce the same thing as %10.2f, %6.3d and also the same as %10.2f, %7.3d...it doesn't change the spacing until I get to %10.2f, %11.3d. It's as if the second argument has to be greater than the first.

Jan 2013-1-30

As the documentation explains accurately, the value before the dot is the "field width", and the value after the point the "precision". If a number has more digits, caused by its value and the precision, than allowed by the field width, more digits are written. This means, the first value is a "minimal field width" and spaces are used for padding on demand.

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