How to Resolve \"Undefined Reference to\" Errors When Linking Static C Libraries with C Code?

undefined reference to Errors in Linking Static C Library with C Code

When attempting to link a static C library with C code, you may encounter "undefined reference to" errors, despite modifying the link order. This issue arises from the differing symbol names created by C and C compilation known as 'name mangling'.

In C , the linker displays demangled symbol names in error messages, which can be confusing. Inspecting the object file (*.o) with "nm -u" reveals that the referenced symbol names do not match those in the library.

To resolve this issue, functions linked in as externals that were compiled using the C compiler must have their function declarations enclosed in an "extern "C" {}" block. This suppresses C name mangling for everything within the block.

For example:

<code class="cpp">extern "C" {
    #include <dual/xalloc.h>
    #include <dual/xmalloc.h>
}</code>

Alternatively, you can wrap function declarations in header files as follows:

<code class="cpp">#if defined (__cplusplus)
extern "C" {
#endif

/*
 * Put plain C function declarations here ...
 */

#if defined (__cplusplus)
}
#endif</code>

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