python 调用C++动态库所遇到的undefined symbol ***

因为算法效率问题所以要在python中调用C,
先写一个C函数:

test.cpp 

# include<stdio.h>
# include <stdlib.h>     //atoi
# include <string.h>    //strlen
# include <unistd.h>   //gethostname()
# include <stdint.h>   //uint64_t

int add(int a,int b){
    printf("this is from C dll");
    return a+b;
}

编译 :

gcc -c -fPIC test.cpp

gcc -shared test.o -o test.so

然后在python中调用sum函数:
mylib.py

from ctypes import *
libc=CDLL("test.so")
libc.sum(2,2)

运行:

python mylib.py

出错:******can not find symbol sum

发现是因为c++编译后的文件会把函数名改名（为了实现重载功能）

用extern “C”声明后，就会使用c的方式进行编译，编译后的文件中仍然是定义的函数名

所以只要讲c库中的代码改为:

# include<stdio.h>
# include <stdlib.h>     //atoi
# include <string.h>    //strlen
# include <unistd.h>   //gethostname()
# include <stdint.h>   //uint64_t
extern "C"{
int sum(int,int);

}

int sum(int a,int b){
        printf("this is from C dll");
        return a+b;
}