BL51: Warning L2: Unresolved External for Functions in C Runtime Lib

Information in this article applies to:

• C51

SYMPTOMS

When I build my project, I receive the following linker warning:

WARNING L2: REFERENCE MADE TO UNRESOLVED EXTERNAL.

The segment name is:

?C?ILDOPTR

which I do not recognize.

CAUSE

This segment is a library routine that your program utilizes. For some reason, the linker cannot find the library which contains this routine.

RESOLUTION

Make sure, in the linker options you have not specified the NODEFAULTLIBRARY directive. In µVision options, this would be placed in Options for Target ... - BL51 Misc - Mics controls field. Using that directive causes the BL51 linker to ignore the standard C51 libraries.

If that does not work, try re-installing the Keil C51 tool package. It may be that one of the .LIB files was accidentally deleted or has become corrupted.

MORE INFORMATION

• Refer to NODEFAULTLIBRARY in the BL51 User's Guide.
• Refer to Warning L2 in the BL51 User's Guide.

SEE ALSO

• BL51: Not Finding Some Functions in Libraries

Last Reviewed: Thursday, February 25, 2021