C function triggers linker error when file renamed to cpp

[danibootstrap]

Hello, I am getting a linked error when I changed file name to cpp. 1>main.obj : error LNK2019: unresolved external symbol "void __cdecl func_name(double * *,int,int,int,double * *,double * *,double * *,double * *)" I am using objects in my new code but this function which was there earlier is triggering this error.How do I handle it? Someone please let me know.

[danibootstrap]

I changed the include file name from .c to .cpp but now I get different errors. I get this
error C2664: 'func_name2' : cannot convert parameter 4 from 'scal (__cdecl *)(scal,scal)' to 'scal (__cdecl *)(void)'

what shall I do?

[danibootstrap]

The follwoing is the function definition

void mat_apply_fx(mat M, int rows, int cols, scal (*fx)(void *), scal par)
{
    int i,j;

    for (i=0; i<rows; i++)
        for (j=0; j<cols; j++)
            M[i][j] = (*fx)(M[i][j], par);
}

the following is the call
mat_apply_fx(W, rows, rows, fx_rand(), 0);

Could some one tell me how to fix this error. Surely renaming the file from c to cpp did some thing (may be it added extra rules on how functions can be prototyped).

[rubberman]

It seems your code has defined the function pointer that returns scal has no matching version that takes a void* argument. Post the function declarations that may be relevant.