so 库加载 __attribute__((constructor))

动态库生成: 

gcc -Wall -shared -fPIC -o libss.so libss.c // 库名和源文件自定义

动态加载：

#include <dlfcn.h>


       void *dlopen(const char *filename, int flag); // filename 动态库名（如libss.so），flag为 RTLD_NOW 或 RTLD_LAZY，RTLD_NOW 库中的所有函数在dlopen返回前都加载，

                                                                     // RTLD_LAZY 库中的函数在用时才加载


       char *dlerror(void);  // dlopen dlsym dlclose的执行若有错误，返回描述错误的字符串


       void *dlsym(void *handle, const char *symbol); //返回函数指针


       int dlclose(void *handle); // 卸载库


       Link with -ldl.

例：

udlopen.c

#include <stdio.h>#include <string.h>#include <dlfcn.h>int main(int argc, char **argv){void (*print)();int (*add)(int, int);void *handle;if (argc < 2)return -1;handle = dlopen(argv[1], RTLD_LAZY);if (!handle) {printf("dlopen failed: %s\n", dlerror());return -1;}print = dlsym(handle, "print");if (!print) {printf("dlsym failed: %s\n", dlerror());return -1;}print();add = dlsym(handle, "add");if (!add) {printf("dlsym failed: %s\n", dlerror());return -1;}add(1, 2);dlclose(handle);return 0;}

libss.c

#include <stdio.h>#include <string.h>void print() {printf("I am print\n");}int add(int a, int b){printf("Sum %d and %d is %d\n", a, b, a + b);return 0;}//static void king() __attribute__((constructor(101))); the following is also rightstatic __attribute__((constructor(101))) void king(){printf("I am king\n");}

编译执行：
gcc -Wall -shared -fPIC -o libss.so libss.c -ldl

gcc -Wall -o udlopen udlopen.c

./udlopen libss.so

I am king
I am print
Sum 1 and 2 is 3