VHDL中文件读取错误

Question

这不起作用。每当我将变量line_content：string（1到4）更改为string（1到20）时，似乎都会出现错误。

它表示存在断言失败：字符串读取失败。 断言失败了。 模拟失败。

LIBRARY ieee; 
USE ieee.std_logic_1164.ALL;
use STD.textio.all; 

ENTITY read_file IS
END read_file;

ARCHITECTURE beha OF read_file IS 

BEGIN
-- Read process
    process 
      file file_pointer : text;
      variable line_content : string(1 to 20);
      variable line_num : line;

    begin
        --Open the file read.txt from the specified location for reading(READ_MODE).
      file_open(file_pointer,"1.txt",READ_MODE);    
      while not endfile(file_pointer) loop --till the end of file is reached continue.
        readline (file_pointer,line_num);  --Read the whole line from the file
        --Read the contents of the line from  the file into a variable.
        READ (line_num,line_content); 
            report line_content;
      end loop;
      file_close(file_pointer);  --after reading all the lines close the file.  
        wait;
    end process;
end beha;