g++ 编译.o目标文件出错，不知什么原因？
say.h
程序代码：#include <iostream>
void sayhello(void);
class Say
{
private:
char * string;
public:
Say( char * str)
{
string = str;
}
void sayThis(const char * str)
{
std::cout << str << "from a static library\n";
}
void sayString(void);
};
~
~
~ -----------------------------------------
say.cpp
程序代码：
#include "say.h"
void Say::sayString()
{
std::cout << string << "\n";
}
Say librarysay("library instance of Say");
~
~
--------------------------------------------
sayhello.cpp
程序代码：#include "say.h"
void sayhello()
{
std::cout << "hello from a static library\n";
}
+++++++++++++++++++++++++++++++++++++++++++++
以下是报错：
Ubuntu 环境 g++
-virtual-machine:~/桌面/CLearning$ g++ say.cpp
say.cpp:7:41: warning: ISO C++ forbids converting a string constant to ‘char*’ [-Wwrite-strings]
Say librarysay("library instance of Say");
^
/usr/lib/gcc/x86_64-linux-gnu/7/../../../x86_64-linux-gnu/Scrt1.o：在函数‘_start’中：
(.text+0x20)：对‘main’未定义的引用
我想把 say.cpp 和 sayhello.cpp编译成目标文件，然后做成静态库，可是一编译就报错了，新手不知什么原因？？
