gcc是编译c语言的，默认情况下，如果直接编译c++程序，会报错：

[root@server demo2]# ls
hello.cpp
[root@server demo2]# cat hello.cpp 
#include <iostream>
using namespace std;
int main(){
  cout<<"hello,c++"<<endl;
  return 0;
}
[root@server demo2]# gcc -o hello hello.cpp 
/tmp/ccAa6oYP.o: In function `main':
hello.cpp:(.text+0xa): undefined reference to `std::cout'
hello.cpp:(.text+0xf): undefined reference to `std::basic_ostream<char, std::char_traits<char> >& std::operator<< <std::char_traits<char> >(std::basic_ostream<char, std::char_traits<char> >&, char const*)'
hello.cpp:(.text+0x14): undefined reference to `std::basic_ostream<char, std::char_traits<char> >& std::endl<char, std::char_traits<char> >(std::basic_ostream<char, std::char_traits<char> >&)'
hello.cpp:(.text+0x1c): undefined reference to `std::ostream::operator<<(std::ostream& (*)(std::ostream&))'
/tmp/ccAa6oYP.o: In function `__static_initialization_and_destruction_0(int, int)':
hello.cpp:(.text+0x4a): undefined reference to `std::ios_base::Init::Init()'
hello.cpp:(.text+0x59): undefined reference to `std::ios_base::Init::~Init()'
collect2: error: ld returned 1 exit status

我们可以通过增加参数-lstdc++来编译，结果如下：

[root@server demo2]# gcc -o hello hello.cpp -lstdc++
[root@server demo2]# ls
hello  hello.cpp
[root@server demo2]# ./hello 
hello,c++
[root@server demo2]# 
如果编译c++程序，可以直接通过g++命令来编译，如下：

可以使用更简单的，直接g++ hello.cpp，这样生成的文件就是a.out

[root@server demo2]# g++ hello.cpp 
[root@server demo2]# ls
a.out  hello.cpp
[root@server demo2]# ./a.out 
hello,c++
[root@server demo2]# 

多个文件编译：准备circle.h,circle.cpp,main.cpp

circle.h

#ifndef CIRCLE_H
#define CIRCLE_H
class Circle{private:double r;public:Circle();Circle(double r);double area();
};
#endif

circle.cpp

#include "circle.h"
Circle::Circle(){this->r = 5;
}Circle::Circle(double r){this->r = r;
}double Circle::area(){return 3.14*r*r;
}

main.cpp

#include <iostream>
#include "circle.h"
using namespace std;int main(){Circle c(3);cout<<"area => "<<c.area()<<endl;return 0;
}

多个文件编译，使用gcc编译，就类似这样：gcc -o main main.cpp circle.cpp -lstdc++，该命令编译中，文件不能带上circle.h头文件，否则会报错。

[root@server demo1]# ls
circle.cpp  circle.h  main.cpp
[root@server demo1]# gcc -o main main.cpp circle.cpp -lstdc++
[root@server demo1]# ls
circle.cpp  circle.h  main  main.cpp
[root@server demo1]# ./main
area => 28.26
[root@server demo1]# 

使用g++编译：可以带上头文件circle.h

[root@server demo1]# ls
circle.cpp  circle.h  main.cpp
[root@server demo1]# g++ -o main2 main.cpp circle.h circle.cpp
[root@server demo1]# ls
circle.cpp  circle.h  main2  main.cpp
[root@server demo1]# ./main2 
area => 28.26
[root@server demo1]#