MATLAB: Output of sprintf – string

MATLABmatlab function

Hi everyone,

on Matlab's documentation I read that sprintf is a function which takes as input data and returns a string. If I write:

x=sprintf('%d',2222)

the output has 1×4 dimension, thus is a character array and not a string (i use Matlab 2015). Why?

Thank you.

Best Answer

Because MATLAB only introduced the string class in R2016b, but previously any character array with size 1xN was called a "string". So for historic reasons there are many references to "strings" that are actually references to 1xN char arrays.

For example this includes the functions sprintf, cellstr, and iscellstr.

For the function sprintf:

Versions R2016a and before: The output is a 1xN char array.
Versions R2016b and later: The output class is the same as that of the first input.

https://www.mathworks.com/examples/matlab/mw/matlab-ex32410134-create-string-arrays

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https://www.mathworks.com/help/matlab/characters-and-strings.html

In a nutshell:

single quotes define a character vector with size 1xN, where N is the number of characters between the quotes.
double quotes define a string array with size 1x1 (i.e. scalar, regardless of how many characters it has). You can think of string arrays as a kind of container for character vectors.

String arrays have some advantages, such as it is possible to have text data with exactly the same dimensions as corresponding numeric data, and there also exist many overloaded operations which perform useful implcit operations on strings. However they also require more memory, can be slower than using character vectors, and are not supported on MATLAB versions prior to R2016b.

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In many situations where a character vector can be used a string scalar is also supported: read the online documentation for the specific functions to know what inputs it accepts. Providing a string/character vector can make a difference: for example, sprintf will return an output of the same class as its formatSpec input argument.

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You can't. For matlab, each character is the same as single number and as you know you can only have one number per matrix element.

You can however store a whole matrix or char in a single cell of a cell array:

>>c = {'a string', 2; [1 2; 3 4], 'another string'};
>>c{1,1}
ans = 
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Or, since r2016b, you can have an array of string objects. Such an array can only contain strings however:

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s =  
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    "a string"       "another string"
    "yet another"    "final one"

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