Matlab coder - When input a filename as input paremeter, how to define input types

Hello, I wonder how could I set the filename as a input parameter? I am using Matlab coder to generate a c++ function, the input parameter is the filename of a image file. I called the parameter in "imread()".

When I use "Autodefine Input Types", the autodefined type is char(1x9) or char(1x:9), which is of course wrong because I can't promise that the length of other filename is smaller than 9.

Then I wanna change the input type to "string(1x1)", the app automatically add a sub-type, like shown in picture below.

According to the request of the app, this sub-type can only be defined as "char", so I choose char(1x1).

Then it goes wrong when generating trial code, saying "The filename or URL must be char vector."

I wonder how could I set the filename as a input parameter? Or if I use char(1xinf) as a input type, how should I define the input parameter in C++ program?(I tried char s[] but faild). Thank you!

[Adam]

Isn't 1xInf an option for the size of a char like it would be for a double?

[Xuechu Xu]

Actually I don't know aobut it, I thought it might be like a malloc command in C file. Do you know how to solve this problem for defining a string with undetermined length as function input? Thank you!

[Adam]

I don't generally pass strings into a Coder app so that is why I was asking if 1xInf isn't an option. It is for doubles so I don't see why it wouldn't be for chars too, though I guess you may want to pass in a variable with the actual length of it also so the C code knows how long it is.