PRB: Inline Assembly C++ Function May Need Return Statement

• Microsoft C/C++ for MS-DOS, version 7.0
• Microsoft Visual C++ for Windows, versions 1.0 and 1.5
• Microsoft Visual C++, 32-bit Edition, versions 1.0 and 2.0

SYMPTOMS

C++ functions containing inline assembly routines that store the return value in the AX register may need a return statement added to the function. If the function does not have a return statement, the following error is generated:

   C2561: 'function name' function must return a value

RESOLUTION

To resolve this error, create a temporary variable and move the AX register to this variable for the return statement. This will work around the C++ type-checking syntax. If you are using C++ version 8.0 that ships with Visual C++ for Windows NT, then the EAX register must be used instead.

Sample Code

/* Compile options needed: none
*/

int func(void)

  //int a;         //Remove this comment to eliminate the error.
  __asm
  {
    mov ax, 02h
    ;mov a, ax         //Remove this comment to eliminate the error.
  }
  //return a;         //Remove this comment to eliminate the error.
}

void main(void)

  int a;
  a = func();