Problematic macro

#define gen_uxtobstr(size) \char* u##size##tobstr(uint##size##_t n) { \        int i; \        for (i = 0; i <  ##size; i++) \        bstr_buf[i] = (n & 2 >> i) ? '1' : '0'; \        bstr_buf[##size] = '\0' \        return &bstr_buf; \}