C++动态链接库实践

参考：https://www.cnblogs.com/Anker/p/3746802.html

gcc -fPIC -shared calc.c -o libcalc.so， 编译得到

 

 在linux上 man dlopen可以得到以下信息：

头文件注释：

 

实践内容：

 

#include <stdio.h>
#include <stdlib.h>
#include <dlfcn.h>

//动态链接库路径
#define LIB_CACULATE_PATH "/home/dahui/work/workspace/CStudy/src/libcalc.so"

//函数指针
typedef int (*CAC_FUNC)(int, int);

int main(void) {

    printf("!!!Hello World!!!\n"); /* prints !!!Hello World!!! */

    void *handle;
    char *error;
    CAC_FUNC cac_func = NULL;

    //打开动态链接库
    handle = dlopen(LIB_CACULATE_PATH, RTLD_LAZY);
    if (!handle) {
        fprintf(stderr, "%s\n", dlerror());
        exit(EXIT_FAILURE);
    }

    //清除之前存在的错误
    dlerror();

    //获取一个函数
    *(void **) (&cac_func) = dlsym(handle, "add");
    //cac_func = (CAC_FUNC) dlsym(handle, "add");
    if ((error = dlerror()) != NULL) {
        fprintf(stderr, "%s\n", error);
        exit(EXIT_FAILURE);
    }
    printf("add: %d\n", (*cac_func)(2, 7));

    cac_func = (CAC_FUNC) dlsym(handle, "sub");
    printf("sub: %d\n", cac_func(9, 2));

    cac_func = (CAC_FUNC) dlsym(handle, "mul");
    printf("mul: %d\n", cac_func(3, 2));

    cac_func = (CAC_FUNC) dlsym(handle, "div");
    printf("div: %d\n", cac_func(8, 2));

    printf("!!!Hello World!!!"); /* prints !!!Hello World!!! */

    //关闭动态链接库
    dlclose(handle);
    //exit(EXIT_SUCCESS);

    printf("!!!Hello World!!!"); /* prints !!!Hello World!!! */

    return EXIT_SUCCESS;
}

输出：