Reading text length in Vivado - vhdl

Question

I need to get the length of a text file in Vivado during simulation. I tried below piece of code but I got an error.
file my_input : TEXT open READ_MODE is "/home/sukru/MD5.dat";
variable my_line : LINE;
variable input_line : LINE;
variable length : integer;
readline(my_input, input_line);
read(input_line, length);
writeline(output, input_line); -- optional, write to std out
write(input_line, integer'(length));
writeline(output, input_line);
The error message is this.
Error: TEXTIO function READ: read a non-integer, an integer is expected
a
-2147483648
I can read text's index but the length is non-sense value. Someone direct me how can I get the length of any text file.

Answer 1

VHDL at present has no way of interfacing to the host operating system to determine a file length.
There's an equivalency between bytes and the VHDL type character (see IEEE Std 1076-2008).
Normative references
...
ISO/IEC 8859-1:1998, Information technology—8-bit single-byte coded graphic character sets—Part 1: Latin alphabet No. 1.
Also see 16.3 Package standard, type character where all 256 enumeration values for a single-byte character are included.
That means we can count characters in a file:
use std.textio.all;
entity length_in_bytes is
end entity;
architecture foo of length_in_bytes is
impure function file_length (file_name: string) return integer is
type char_file is file of character;
file file_in: char_file open read_mode is file_name;
variable char_buffer: character;
variable length: integer := 0;
begin
while not ENDFILE(file_in) loop
read(file_in, char_buffer);
length := length + 1;
end loop;
file_close(file_in);
-- report file_name & " length = " & integer'image(length);
return length;
end function;
signal filelength: natural;
begin
filelength <= file_length("md5.dat");
process
begin
wait for 0 ns; -- skip default signal value;
report "file md5.dat length = " & integer'image(filelength);
wait;
end process;
end architecture;
The length returned by the function call will match the length the host operating system provides.
The file_close leaves the file unlocked for further use and reads of an open file are sequential from file open.

Answer 2

This line reads a line from the file:
readline(my_input, input_line);
This line tries to read an integer (destructively) from the line:
read(input_line, length);
It doesn't return the length of the file (or the line). You don't supply the file you are trying to read (it would have been better had you done so - see this ), but my guess is that it doesn't contain an integer and hence your error message.
If you want to get the length of any text file, you need to read every line in the file, find each's length and add them. It is easy to find the length of each line, because type line does have a 'length attribute, so the length of each line will be:
input_line'length
(Though note that the 'length attribute does not include the end-of-line character.) By the way, this line won't display what you've just read, because the read (if successful) is destructive:
writeline(output, input_line); -- optional, write to std out
(A "destructive read" is a read which removes the data as well as reading it.)