save does not recognize text scalar
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The following code snippet fails unexpectedly:
clear;
myFilename = 'SavedData';
mustBeTextScalar(myFilename); % Throws exception if not true.
x = 3;
save(myFilename, x);
The variable myFilename passes the mustBeTextScalar as expected. However, the save command fails with the message
Error using save
Argument must be a text scalar.
Error in
saveTest (line 5)
save(myFilename, x);
^^^^^^^^^^^^^^^^^^^
QUESTION: Why does save not see myFilename as a text scalar, even though mustBeTextScalar passes it?
[MATLAB Version: 25.1.0.2943329 (R2025a)]
采纳的回答
Fangjun Jiang
2025-7-24
编辑：Fangjun Jiang
2025-7-24
0 个投票
It is not about the variable name myFilename.
save(myFilename)
or
save(myFilename,'x')
4 个评论
Richard
2025-7-24
Walter Roberson
2025-7-24
Right.
save() permits non-constant expressions to be passed as the variable names. You can compute the names of the variables to save.
But more directly: the parsing of
save(myFileName,x)
has to follow the regular rules of MATLAB expressions. MATLAB interprets all function parameters before paying attention to the function being called. So myFileName is first looked up in context and the pointer to the text vector is prepared on the stack.Then, in this hypothetical context, the content of x would be looked up and the pointer to the numeric scalar would be prepared on the stack. Then save() would be called with those two items on the stack. save() would receive first the pointer to the text vector and then the pointer to the numeric scalar. But in doing so it would have lost the name of the numeric scalar and would only have its value.
This is why save() needs text vectors containing the names of variables to be saved, instead of needing the content of those variables.
Stephen23
2025-7-25
"...But in doing so it would have lost the name of the numeric scalar and would only have its value. This is why save() needs text vectors containing the names of variables to be saved, instead of needing the content of those variables."
Yet TABLE manages to do this, so it turns out that functions do not "need" text inputs like this.
Well, table() uses inputname under the hood, and invents variable names for cases where expressions were passed. save() does not have the luxary of being able to invent variable names.
x = [1;2;3];
table(x, [4;5;6], +x)
... variable names are used where inputname() is able to figure them out, and otherwise variable names are invented for expressions.
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