CODEWITHSUNDEEP
c++clinkerc++-cliextern
user7664179
user7664179

Reputation:

LNK2019: Unresolved external symbol in C++/CLI

I have a sample.c file where a non-static function is defined

Source: sample.c

#if defined(__cplusplus)
extern "C" {
#endif

int get_sample_value()
{
    return 1000;
}

#if defined(__cplusplus)
}
#endif

There is pure C++ SDK project, sample_sdk which basically generates a couple of static-libs, where get_sample_value() function is used within one of the source files as follows:

Source: sample_sdk_source.cpp

extern int get_sample_value();

static void do_processing()
{
    int sample_value = get_sample_value();
    process( sample_value );
}

Above-mentioned sample.c will be compiled in another C++/CLI GUI application, SampleViewer where sample_sdk libs are included within this application. But when compiling the SampleViewer we are getting the following error:

libsample-sdk-x86.lib(sample_sdk_source.obj) : error LNK2019: unresolved external symbol "int __cdecl get_sample_value()" (?get_sample_value@@YAPBUint@@XZ) referenced in function "public: static void __cdecl do_processing()" (?do_processing@@SAXXZ)

I also tried to use the same function from SampleViewer::main.cpp file, but the same error exists. Is there any issue when accessing function defined in C file as extern from C++/CLI environment?

Upvotes: 1

Views: 619

Answers (1)

Botje
Botje

Reputation: 30807

The linker error says it all:

  • Your extern int get_sample_value(); declaration in C++ sets up an undefined symbol for the mangled name ?get_sample_value@@YAPBUint@@XZ
  • Your definition in sample.c defines a symbol with a non-mangled name (_get_sample_value).

To solve this, either mark your declaration in C++ with extern "C" as well, or better yet: move the declaration into a header that both sample.c and sample_sdk_source.cpp can include (with the #if defined(__cplusplus) guard)

Upvotes: 2

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