Parsing text without eval

Nieves Lopez

2023 3 21

2 个回答

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Hello,

I have some strings with values that I would like to parse. The easiest way is to use the eval function. However, I can not use it since the code is going to be compiled. Any idea on how to do this without having to parse each of the characters?

As an example, one of the string could be like this:

>> text = '{[1 2], [3 4] ''someText'' {5, [6, 7]}}'

text =

{[1 2], [3 4] 'someText' {5, [6, 7]}}

>> eval(text)

ans =

1×4 cell array

[1×2 double] [1×2 double] 'someText' {1×2 cell}

Thank you in advance!

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Rik 2023-3-21

在 MATLAB Online 中打开

Your requirements seem to conflict. You want to evaluate arbitrary code, but you don't want to use the function that evaluates arbitrary code.

Even if you use the recently introduced option to restrict what str2num does (to make it safer than eval) it will fail on more complicated things like you posted.

text = '{[1 2], [3 4] ''someText'' {5, [6, 7]}}'
text = '{[1 2], [3 4] 'someText' {5, [6, 7]}}'
X = str2num(text,Evaluation="restricted")
X =

     []

I suspect you will have to write you own parser.

Nieves Lopez 2023-3-21

Not so arbitrary code, only with numbers, strings, cells. No function calls. I was just wondering if I'm missing any function that can help me.

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回答（2 个）

Adam Danz 2023-3-21

在 MATLAB Online 中打开

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You could write the string to an m-file and then run the m-file, though this has the same flaws/risks as eval.

This demo creates a file temp.m, writes the string text to the file, runs the file, and then deletes the temporary file.

text = '{[1 2], [3 4] ''someText'' {5, [6, 7]}}'
tempFile = 'temp.m';
fid = fopen(tempFile,'w'); 
fidCleanup = onCleanup(@()fclose(fid));
fprintf(fid,'%s',text); 
clear fidCleanup
run(tempFile)
delete(tempFile)

Result

ans =

1×4 cell array

{[1 2]} {[3 4]} {'someText'} {1×2 cell}

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Nieves Lopez 2023-3-21

Thank you again for your response. In the code, when Matlab runs tempFile it only shows the filename by the command window (as the content of any other variable). Anyway, when generating code in C with codegen, the compiler would look for a file named temp.m and would not find it.