How to specify (const char *) type in xml

Hello Everyone.

I have made an OOT module gr-ldpc. The ldpc encoder loads the parity
matrix data from a file. The constructor of this class takes as input
file name as parameter of type " const char * ".

I used following in param sector in the xml file.

File alist_file const char * --------------------------------------------------------

I also tried using the following

File alist_file str ----------------------------------------------------------

To specify the file in the encoder block (in grc) I made a variable
and specified the file name within double quotes “file_name”, and used
variable_id in place of the corresponding parameter in the encoder
In both the cases the block is colored red and I can’t run the

What could I use to specify the file name?

Got fixed when I used file_open type.