Matlab coder num2str not supported

Question

I am trying to convert a Matlab project into C++ by using Matlab coder. I have few places in my code that I use num2str function. But when trying to build the project using Matlab coder I get the following error.

"The function 'num2str' is not supported for standalone code generation."

I used this function in cases where I needed to create a field identifier for structs.

Eg:

for i=1:numel(bvec)
      fId = ['L', num2str(i)];
      tmp = mystruct.(fId);  
      % do some work here  
end

Is there an alternative to the function num2str for me to be able to convert the project?

@excaza thats not supported, List of supported functions, fprintf is supported, with lots of contraints... — RTL
– RTL, Commented Aug 27, 2014 at 12:36
Well, the constraints are not that unexpected. The function behaves more like c than matlab, so in most cases a c call should do the trick. — patrik
– patrik, Commented Aug 27, 2014 at 13:04
Would you be able to convert it to its corresponding unicode values you think? The you would be able to cast it. It is a bit of a detour, but it should at least work. The problem is not very hard though, you can have a list of unicode characters in a vector. Set the corrensponding values in the right places so that a call uniVec(3) will return the unicode value for 3 for example. Also you will have to handle the case of numbers with more than 1 digit in some way. — patrik
– patrik, Commented Aug 27, 2014 at 13:19
You have a bigger problem, which is that dynamic field names aren't supported by MATLAB Coder either. — Sam Roberts
– Sam Roberts, Commented Aug 27, 2014 at 14:34

sclarke81 · Accepted Answer · 2014-08-27 14:39:59Z

4

Using sprintf would be easy but I'm not sure if you can use it?

fId = sprintf('L%d', i);

If numel(bvec) is in the range 0 to 9 you could use char:

fId = ['L', char(48+i)];

Or you could create your own number to string conversion function. There may be better ways, but here's an idea:

function s = convertnum(n)
   if n > 9
      s = [convertnum(floor(n/10)), char(48+mod(n,10))];
   else
      s = char(48+n);
   end
end

Then use it like this:

fId = ['L', convertnum(i)];

EDIT

An alternative conversion function based on comments:

function s = convertnum(n)
   s = [];
   while n > 0
      d = mod(n,10);
      s = [char(48+d), s];
      n = (n-d)/10;
   end
end

edited Aug 27, 2014 at 14:39

answered Aug 27, 2014 at 14:04

sclarke81

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5 Comments

patrik Over a year ago

sprinf is not supported. Otherwise, nice solution to convert the numbers to ascii. However, it think that a for loop would be sufficient. This is easy to loop and a would not be hard to read. That would really be the only reasons to use recursion since it is a known problem that recursion is inefficient in terms of calculation time.

sclarke81 Over a year ago

Thanks @patrik I've added a looped version as well.

suranga Over a year ago

@sclarke81 Yes. It's working. This is the best solution for me at the moment. Thanks

suranga Over a year ago

@sclarke81 Oops.. Now I get a new problem in code generation readiness issues. "Recursive functions like convertnum.m are currently unsupported for code generation."

patrik Over a year ago

This may very well be the only solution. And it is really no magic to it. This is the most fundamental way to create a char and is based on the way a char is stored in memory.

Kobi Mamo · Accepted Answer · 2016-04-11 13:27:13Z

I wrote the following code for Matlab2016a Coder to replace num2str, it also supports double precision:

function str = DoubleArray2String(x)
    str_cell=cell(1,length(x));
    for i=1:length(x)
        n = x(i);
        l = fix(n);
        r = n-l;
        str_cell{i} = strjoin({Double2String(l),Reminder2String(r)},'.');
    end
    str = strjoin(str_cell,',');
end

function str = Double2String(n)
    str = '';
    while n > 0
        d = mod(n,10);
        str = [char(48+d), str];
        n = (n-d)/10;
    end
    if isempty(str)
        str='0' ;
    end
end

function str = Reminder2String(n)
    str = '';
    while (n > 0) && (n < 1)
        n = n*10;
        d = fix(n);
        str = [str char(48+d)];
        n = n-d;
    end
    if isempty(str)
        str='0' ;
    end
end

Ruchir · Accepted Answer · 2015-09-16 09:40:39Z

0

A function equivalent of Matlab's num2str can be written using to_string in C++. Please see my version of the function:

#include"stdafx.h"
#include <sstream>
#include <string.h>

using namespace std;

string num2str(int number)
{
    string s;
    s = to_string(number);
    return s;
}

answered Sep 16, 2015 at 9:40

Ruchir

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