Why the type converter does not work ?

[Altera_Forum]

In my design I need to do is convert a std_logic_vector signal to the integer signal for array index. Then I do following: 

"   use IEEE.NUMERIC_STD.ALL;   generic  ( C_SLV_ADWIDTH : integer := 6; -- This width is actual address width  )    constant C_NUM_REG : integer := 2 ** C_SLV_ADWIDTH;    signal slv_addr : std_logic_vector(C_SLV_ADWIDTH-1 downto 0);  signal slv_addr_integer : integer range 0 to C_NUM_REG;     slv_addr_integer <= to_Integer(slv_addr); -- this convert data type std_logic_vector to integer  " But I get errors, why converter does not work?    Thanks in advance. 

[Altera_Forum]

--- Quote Start ---  In my design I need to do is convert a std_logic_vector signal to the integer signal for array index. Then I do following: "   use IEEE.NUMERIC_STD.ALL;   generic  ( C_SLV_ADWIDTH : integer := 6; -- This width is actual address width  )    constant C_NUM_REG : integer := 2 ** C_SLV_ADWIDTH;    signal slv_addr : std_logic_vector(C_SLV_ADWIDTH-1 downto 0);  signal slv_addr_integer : integer range 0 to C_NUM_REG;     slv_addr_integer <= to_Integer(slv_addr); -- this convert data type std_logic_vector to integer  " But I get errors, why converter does not work?    Thanks in advance.   --- Quote End ---    to_integer(unsigned(x)); or to_integer(signed(x));  The choice is yours. I think you want the first

[Altera_Forum]

Thanks very much, kaz. Yes, I want the first. I try what you suggested and it works.

[Altera_Forum]

--- Quote Start ---  Thanks very much, kaz. Yes, I want the first. I try what you suggested and it works.  --- Quote End ---    Great. Now it is your turn to explain to te forum why you need to cast unsigned (or signed) for std_logic.

[Altera_Forum]

I define an new type which is an array: 

 type array_reg is array (C_NUM_REG-1 downto 0) of std_logic_vector (C_SLV_DWIDTH-1 downto 0);  Then I declare a signal:  signal slv_reg : array_reg;  slv_reg will be used as a group of registers whose number will be small, like 32, 64. Then I want to use input signal "slv_addr" as the address to reach the register. So I try to convert it to "slv_addr_integer " then use it as:  a<=slv_reg(slv_addr_integer);