Q59086: Error C2094: Label "xxx" Was Undefined

Article: Q59086
Product(s): See article
Version(s): 2.00 2.01 2.50 2.51
Operating System(s): MS-DOS
Keyword(s): ENDUSER | s_quickasm S_C | mspl13_c
Last Modified: 18-NOV-1990

The following error occurs with inline assembly if one of the operands
is a hexadecimal value that starts with an alphanumeric character
(A-F, a-f):

   error C2094 : label 'xxx' was undefined

Sample Code
-----------

void main(void)
{
   _asm mov ah, f0h
}

This is expected behavior in inline assembly since "f0h" is a valid C
variable and it is also a valid label name. In the sample code, since
"f0h" was not declared as a variable and there is no label defined as
"f0h", the compiler returns with an error C2094.

To use a hexadecimal value that starts with an alphanumeric character
into a register, there are two options as follows:

1. Assign the value to a variable, then move the contents of the
   variable into the register, as follows:

      unsigned char hex_value = 0xf0;
      void main (void)
      {
         _asm mov ah, hex_value
      }

2. Instead of using Assembler notation (F0h), use C notation for
   the hex value, as follows:

      void main(void)
      {
         _asm mov ah, 0xf0
      }

3. Use a leading 0 (zero) [or multiple leading 0s (zeros)] on the
   MASM-style hex constant. This procedure sets the value for the high
   and low portion of the register, as follows:

      void main(void)
      {
         _asm mov ax, 000f0h
      }

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