Q41578: "st" Is the Floating Point Stack Register in In-Line Assembly

Article: Q41578
Product(s): See article
Version(s): 2.00
Operating System(s): MS-DOS
Keyword(s): ENDUSER | | mspl13_c
Last Modified: 28-FEB-1989

Question:

Why can't I use the variable "st" in a block of in-line assembly code?

Response:

The "st" variable is the floating point stack register and as such is
a reserved name. If you attempt to use this name in an LES or LDS
instruction, you will receive the following error:

   error C2415 : improper operand type

You should not use "st" as a variable name. Choose another name
instead.

The following code generates error C2415 when compiled under any
memory model, at any warning level, and with MS EXTENSIONS enabled:

char * st;           /* st is the floating point stack register */
main() {
  _asm  {
      les  di, st    /* generates the error */
      lds  si, st    /* generates the error */
  }
}

Changing "st" to any other nonreserved name will resolve this
situation.

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