Android JNI加载hal的dlopen()相关操作_编程设计

1.函数集合

#include <dlfcn.h> 
 
void *dlopen(const char *filename, int flag); 
char *dlerror(void); 
void *dlsym(void *handle, const char *symbol); 
int dlclose(void *handle); 

Link with -ldl.

2.Demo例子

caculate.c用于编译成一个库

int add(int a,int b) 
{ 
    return (a + b); 
} 
 
int sub(int a, int b) 
{ 
    return (a - b); 
} 
 
int mul(int a, int b) 
{ 
    return (a * b); 
} 
 
int div(int a, int b) 
{ 
    return (a / b); 
}

main.c调用这个库里面的函数

#include <stdio.h> 
#include <stdlib.h> 
#include <dlfcn.h> 
 
 
#define LIB_CACULATE_PATH "./libcaculate.so" 
 
typedef int (*CAC_FUNC)(int, int); 
 
int main() 
{ 
    void *handle; 
    char *error; 
    CAC_FUNC cac_func = NULL; 
 
    handle = dlopen(LIB_CACULATE_PATH, RTLD_LAZY); 
    if (!handle) { 
        fprintf(stderr, "%s\n", dlerror()); 
        return -1; 
    } 
 
    //获取一个函数 
    cac_func = dlsym(handle, "add"); 
    if ((error = dlerror()) != NULL)  { 
        fprintf(stderr, "%s\n", error); 
        return -1; 
    } 
    printf("add: 2+7=%d\n", cac_func(2,7)); 
 
    cac_func = dlsym(handle, "sub"); 
    printf("sub: 9-2=%d\n", cac_func(9,2)); 
 
    cac_func = dlsym(handle, "mul"); 
    printf("mul: 3*2=%d\n", cac_func(3,2)); 
 
    cac_func = dlsym(handle, "div"); 
    printf("div: 8/2=%d\n", cac_func(8,2)); 
 
    dlclose(handle); 
 
    return 0; 
}

编译执行：

编译： 
$ gcc -rdynamic -o main main.c -ldl 
$ gcc -shared -fPIC caculate.c -o libcaculate.so 
执行： 
$ ./main  
add: 2+7=9 
sub: 9-2=7 
mul: 3*2=6 
div: 8/2=4

或者使用一个结构体将所有的函数包装起来，这样只需要调用一次dlsym()

struct math { 
    int (*add)(int a,int b); 
    int (*sub)(int a,int b); 
    int (*mul)(int a,int b); 
    int (*div)(int a,int b); 
}; 
 
static int math_add(int a,int b) 
{ 
    return (a + b); 
} 
 
static int math_sub(int a, int b) 
{ 
    return (a - b); 
} 
 
static int math_mul(int a, int b) 
{ 
    return (a * b); 
} 
 
static int math_div(int a, int b) 
{ 
    return (a / b); 
} 
 
/*shouldn't be static, else dlsym() couldn't find it*/ 
struct math HMI = { 
    .add = math_add, 
    .sub = math_sub, 
    .mul = math_mul, 
    .div = math_div, 
};

#include <stdio.h> 
#include <stdlib.h> 
#include <dlfcn.h> 
 
struct math { 
    int (*add)(int a,int b); 
    int (*sub)(int a,int b); 
    int (*mul)(int a,int b); 
    int (*div)(int a,int b); 
}; 
 
#define LIB_CACULATE_PATH "./libcaculate.so" 
 
typedef int (*CAC_FUNC)(int, int); 
 
int main() 
{ 
    void *handle; 
    char *error; 
    struct math *hmi; 
 
    handle = dlopen(LIB_CACULATE_PATH, RTLD_LAZY); 
    if (!handle) { 
        fprintf(stderr, "%s\n", dlerror()); 
        return -1; 
    } 
 
    //获取一个函数 
    hmi = dlsym(handle, "HMI"); 
    if ((error = dlerror()) != NULL)  { 
        fprintf(stderr, "%s\n", dlerror()); 
        return -1; 
    } 
    printf("add: 2+7=%d\n", hmi->add(2,7)); 
    printf("sub: 9-2=%d\n", hmi->sub(9,2)); 
    printf("mul: 3*2=%d\n", hmi->mul(3,2)); 
    printf("div: 8/2=%d\n", hmi->div(8,2)); 
 
    dlclose(handle); 
 
    return 0; 
}

3.详细信息：# man dlopen

本文参考链接：https://www.cnblogs.com/hellokitty2/p/10790200.html