About assignment operator over loading error-Collection of common programming errors

Please explain the error message for this program ..

#include 
using namespace std;
class copyConst
{

    private:
    int someVal;
    public:
    copyConst(const copyConst &objParam)
    {
        someVal = objParam.someVal;
    }
    copyConst()
    {
        someVal = 9;
    }
    copyConst& operator=(const copyConst &objParam)
    {
        if (this == &objParam)
            return *this;

        someVal = objParam.someVal;
        return *this;
        }
    };

int main(int argc, char **argv)
{
    copyConst obj1;
    copyConst obj2(obj1);
    copyConst obj3 = obj1;
    copyConst obj4;
    obj4 = obj1;


    return 0;
}

ERROR MESSAGE:

gcc -Wall -o “untitled” “untitled.cpp” (in directory: /home/rwik/Documents) untitled.cpp: In function ‘int main(int, char**)’: untitled.cpp:53:12: warning: variable ‘obj3’ set but not used [-Wunused-but-set-variable] /tmp/ccUIyRPg.o: In function __static_initialization_and_destruction_0(int, int)': untitled.cpp:(.text+0x8a): undefined reference to std::ios_base::Init::Init()’ untitled.cpp:(.text+0x8f): undefined reference to `std::ios_base::Init::~Init()’ Compilation failed. collect2: ld returned 1 exit status

1. There are two type of warning messages. The second one is because of missing linking flag in gcc: gcc -lstdc++ -Wall -o "untitled" "untitled.cpp" (or the equivalent g++ -Wall -o "untitled" "untitled.cpp.

   The first warning regarding unused variable is because of obj3 variable which is declared but not used anywhere else. For such cases I’m using (void)obj3; statement to workaround such warning messages.

2. Compile using g++, not gcc. You have C++ code, not C code.

   It has nothing to do with the class code.

Originally posted 2013-11-09 19:46:06.