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Is it possible to create a structure with fields but without defined values?

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Mr M.
Mr M. on 1 Jul 2015
Answered: Walter Roberson on 2 Jul 2015
Is it possible to create a structure with fields but without defined values? and add values to the structure later?

Answers (2)

Walter Roberson
Walter Roberson on 2 Jul 2015
Muthu's answer is completely correct for producing a structure array with one member with defined fields which have been initialized to [] .
Sometimes, though, what you want is to create a structure with no members but which has defined fields. The method for doing that is not obvious but is
z = struct('fieldname1',{},'fieldname2',{})
the output of that would be a 0 x 0 structure which has the given fields.
Pre-defining an empty structure can be important in some cases involving copying members between structures, or appending structure members. For example, using the z I defined here:
>> cell2mat({[], struct('fieldname1', 3, 'fieldname2', 'hello')})
Error using cell2mat (line 45)
All contents of the input cell array must be of the same data type.
>> cell2mat({z, struct('fieldname1', 3, 'fieldname2', 'hello')})
ans =
fieldname1: 3
fieldname2: 'hello'

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