g++ without libstdc++ - can it be done? - a very configurable lightweight libstdc++ where I can take stuff out easily would also do the trick

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I'm trying something spooky here. I'm trying to write C++ programs, compiled with GNU's g++, but without a dependency on libstdc++ :) but it seems that I need that for even the most basic things need it.

A libstdc++ with a configurable feature set would be acceptable.

The command I use is

g++ -nodefaultlibs -fno-rtti -fno-exceptions -lc

Without libstdc++, I get:

undefined reference to `operator delete(void*)'  
undefined reference to `operator new(unsigned int)'  
undefined reference to `vtable for __cxxabiv1::__class_type_info'  
undefined reference to `vtable for __cxxabiv1::__si_class_type_info'  
undefined reference to `__cxa_pure_virtual'

These aren't in libc, so is there a really light libstdc++ that implements just these things?

My test code which I want to build this way currently looks like this:

#include <stdio.h>

template <class T>
class X
{
    public:
    T a;
};

class A1
{
    public:
        virtual void f() = 0;
        virtual ~A1() {}
};

class A2 : public A1
{
    public:
        virtual void f() {};
        virtual ~A2() {}
};

class Y
{
    public:
        ~Y() {}
};

int main()
{
    X<int> A;
    X<float> B;
    Y *C = new Y;

    A.a = 12;
    B.a = 2.3;

    printf("A: %d; B: %f\n", A.a, B.a);

    A2 *a2 = new A2;
    a2->f();

    return 0;
}
libstdc++ c++
5 Answers

Maybe this answer is a bit too late, but...

Writing c++ programs without libstdc++ is easy. I'm doing it for decades. Just avoid linking with libstdc++. That's easy: either use gcc for linking instead of g++, or provide a fake libstdc++ with only new, del and a few other functions.

Here's a example how you can replace the basic libstdc++ functionality with a transparent wrapper around malloc:

#include <stdlib.h>

// MSVC uses __cdecl calling convention for new/delete :-O
#ifdef _MSC_VER
#  define NEWDEL_CALL __cdecl
#else
#  define NEWDEL_CALL
#endif

extern "C" void __cxa_pure_virtual ()
{
    abort ();
}

void * NEWDEL_CALL operator new (size_t size)
{
    return malloc (size);
}

void * NEWDEL_CALL operator new [] (size_t size)
{
    return malloc (size);
}

void NEWDEL_CALL operator delete (void *p)
{
    if (p) free (p);
}

void NEWDEL_CALL operator delete [] (void *p)
{
    if (p) free (p);
}

void NEWDEL_CALL operator delete (void *p, size_t)
{
    if (p) free (p);
}

Now put that into a file named, say, libstd--.cpp, and build your own libstdc++.a:

gcc -c -O libstdc--.cpp
ar crs libstdc++.a libstdc--.o

Then you can try a simple test:

class A
{
    int *x;

public:
    A () { x = new int [10]; }
    ~A () { delete [] x; }
};

int main ()
{
    A a;
    return 0;
}

Compile and look what's got linked:

g++ -g test.cpp -o test -L.

# ldd ./test
    linux-vdso.so.1 (0x00007ffed0b8d000)
    libm.so.6 => /lib64/libm.so.6 (0x00007f4d18df0000)
    libgcc_s.so.1 => /lib64/libgcc_s.so.1 (0x00007f4d18bd9000)
    libc.so.6 => /lib64/libc.so.6 (0x00007f4d18823000)
    /lib64/ld-linux-x86-64.so.2 (0x00007f4d1913b000)

Hey, look, ma, no libstdc++!

As an alternative, you may avoid using a fake libstdc++ by linking with gcc instead of g++ and by providing libstdc--.o on the linker command line so that your code may find the replacement news and deletes.

user_93602580
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