Changing entry point function

[Premkumar]

a.cpp
----------------------------------
#include <iostream>
using namespace std;

void mymain() {
        cout<<"my-main"<<endl;
}
----------------------------------

I'm trying to start my program at mymain than the standard main ..
So I compiled a.cpp to a.o &

I executed :
g++ -Wl,-emymain  a.o

That did not work as the linker said it could not find the symbol. So
I used name mangler (nm) to demangle a.o
g++ -Wl,-emymain__Fv  a.o

Now the linker says:
/usr/lib/crt1.o(.text+0x18): In function `_start':
: undefined reference to `main'
collect2: ld returned 1 exit status

I also tried the following
g++ -Wl,--verbose -Wl,-emymain__Fv -Wl,--defsym -Wl,start=mymain__Fv
a.o
g++ -Wl,--verbose -Wl,-emymain__Fv -Wl,--defsym -Wl,_start=mymain__Fv
a.o

Still no use..

What mistake am I making here ?