BL51: Error 118 (Erroneous Reference to External Variables)

Information in this article applies to:

• C51 All Versions

QUESTION

The following C file (C:\MYCODE\J1.C)...

/*------------------------------------------------------------/*
extern long Junk;
int junk;

void main (void)
{

for (junk = 0; junk < 100; junk++)
  {
  Junk = 1000L * junk;
  }

}
/*------------------------------------------------------------/*

generates the following error when compiled and linked with the Keil 8051 tools:

*** ERROR 118: REFERENCE MADE TO ERRONEOUS EXTERNAL
    SYMBOL:  JUNK
    MODULE:  C:\MYCODE\J1.OBJ (J1)
    ADDRESS: 0020H

What is wrong?

ANSWER

Your program is technically correct. The problem lies in the object module format of the object files created by the Keil C Compiler.

The object files are created according to the OMF-51 object module format specified by Intel. This object module format does not allow lowercase variable names. Therefore, all public variables are treated as uppercase. When you create 2 public symbols with the same name but with different cases, the linker complained about ERRONEOUS EXTERNALS.

Change the name of one of the variables to avoid this problem.

MORE INFORMATION

• Refer to Error L118 in the BL51 User's Guide.

Last Reviewed: Thursday, February 25, 2021