Why do I get "undefined reference to..." when trying to call a C-function inside a .cpp-file?

[arnold_w]

I am writing code for an ARM processor and compiling with GCC inside Eclipse IDE. My project has 3 files, main.c, myDummyFile.h and myDummyFile.cpp. myDummyFile.h:

#ifndef MYDUMMYFILE_H_
#define MYDUMMYFILE_H_

#ifdef __cplusplus
extern "C" {
#endif

int myDummyFunction();

#ifdef __cplusplus
} //end extern "C"
#endif

#endif /* MYDUMMYFILE_H_ */

myDummyFile.cpp:

#include using namespace std;

// Throw in some C++ syntax to make sure this file is compiled as a C++ file and not as C-file
using cPlusPlusCallback_t = function ;

volatile int preventOptimizationDummy = 0;

int myDummyFunction() {
return preventOptimizationDummy++;
}

main.c:

#include
#include
#include "myDummyFile.h"

int main(int argc, char* argv[]) {
return myDummyFunction();
}

Does anybody know why I get the error message "undefined reference to `myDummyFunction'" when I try to compile this? If I remove the call to myDummyFunction() then it compiles fine so the compiler does seem to be able to compile .cpp-files.

[Lost User]

You need to add the following line to myDummyFile.cpp:

#include "myDummyFile.h"

Otherwise the compiler will generate a decorated* name for myDummyFunction, because the source file is C++ not C. *In C++ external names have additional characters so the linker will not match what is called from your main file.