Why Do I Get 'Undefined Reference' Errors When Linking a Static C Library to C Code?

Undefined Reference Errors When Linking Static C Library with C Code

When linking a C program with a static C library, "undefined reference to" errors can occur even when the library name is specified in the linking command. This issue arises due to differences between C and C compilation processes.

In C , the compiler performs name mangling, which transforms function symbols into mangled names in the object file. However, the C library functions do not undergo name mangling. Thus, the linker faces difficulties in matching the mangled function names in the object file with the unmangled function names in the library, leading to the undefined reference errors.

Solution

To resolve this issue, C programs linking C libraries should use the extern "C" block. This block suppresses name mangling for all declarations and definitions within it. By enclosing the library function declarations in extern "C" blocks, the linker can identify them and resolve the undefined reference errors.

Alternatively, the header file containing the library function declarations can be wrapped in conditional declarations to differentiate between C and C compilation environments. For C compilation, the declarations should be enclosed in extern "C" {} blocks. This ensures name mangling suppression for the library functions and allows successful linking without undefined reference errors.

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