Why does datenum('null','yyyymmdd') return an actual date?

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Jean Dupin 2016-12-21

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回答： Jos (10584) 2016-12-21

As part of date manipulation, I need to convert a whole array of string dates into numbers? This array may sometimes contain 'null' elements which I should probably take out first.

I was just curious to why

datenum('null','yyyymmdd')

returns 736330 (i.e. 01-Jan-16) and doesn't fail? For example,

datenum('null')

would return an error

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Answer 1

Jos (10584) 2016-12-21

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https://ww2.mathworks.cn/matlabcentral/answers/317732-why-does-datenum-null-yyyymmdd-return-an-actual-date#answer_248055

The help of DATENUM states:

Certain formats may not contain enough information to compute a date number. In those cases, hours, minutes, and seconds default to 0, days default to 1, months default to January, and years default to the current year.

Hence the value of 736330. Furthermore, if you do not specify the format identifier (the second argument), the help tells you that

If S is a string, it must be in one of the date formats 0,1,2,6,13,14,15,16,23 as defined by DATESTR.

which is definitely not the case with S being 'null'.