Linux C 动态链接库创建和使用

Linux下C实现的共享库

 

1. 共享库的命名：
 Windows 下的共享库后缀名为*.dll, Linux下共享库以.so结尾
 
2. 如何创建共享库？：
 $>gcc -Wall -fpic -shared mytestso.c -o mytestso.so
 # -fpic: 使输出的对象模块是按照可重定位地址方式生成
 
3. 如何使用共享库？
 3.1 需要事先知道函数名称（字符串）
 3.2 在主程序中加载共享库
 3.3 获取函数的起始地址（函数指针）
 3.4 主程序编译命令
  $>gcc -Wall main.c -ldl -o main
  # -ldl : 表示的对象模块需要使用共享库
  
4. 动态连接加载的编程接口
 #include
 4.1 void *dlopen(const char *filename, int flag);  
 4.2 void *dlsym(void *handle, char *symbol);
 4.3 int dlclose(void *handle);
 4.4 const char *dlerror(void);

// file mytestso.h
#include
                                                                                                                                           
int GetMax(int a, int b);
int GetInt(char* psztxt);
                                                                                                                                           
typedef int GetMax_t(int a, int b);
typedef int GetInt_t(char* psztxt);

// file mytestso.c
int GetMax(int a, int b)
{
    if (a > b)
        return a;
    else
        return b;
}
                                                                                                                                           
int GetInt(char* psztxt)
{
    if ( 0 == psztxt )
    {
        return -1;
    }
                                                                                                                                           
    return atoi(psztxt);
}

// main.c
#include
#include
#include "mytestso.h"
                                                                                                                                           
int main(int argc, char** argv)
{
    void* pdlhandle;
    char* pszerror;
                                                                                                                                           
    int a, b;
    char* psztxt = "1024";
                                                                                                                                           
    // open mytestso.so
    pdlhandle = dlopen("./mytestso.so", RTLD_LAZY);
    if ( 0 != (pszerror = dlerror()) )
    {
        printf("%s\n", pszerror);
        exit(1);
    }
                                                                                                                                           
    // get GetMax func
    GetMax_t* GetMax_Ptr = dlsym(pdlhandle, "GetMax");
    if ( 0 != (pszerror = dlerror()) )
    {
        printf("%s\n", pszerror);
        exit(1);
    }
                                                                                                                                           
    // get GetInt func
    GetInt_t* GetInt_Ptr = dlsym(pdlhandle, "GetInt");
    if ( 0 != (pszerror = dlerror()) )
    {
        printf("%s\n", pszerror);
        exit(1);
    }
                                                                                                                                           
    // call func
    a = 200;
    b = 600;
    printf("max=%d\n", GetMax_Ptr(a, b));
    printf("txt=%d\n", GetInt_Ptr(psztxt));
                                                                                                                                           
    // close mytestso.so
    dlclose(pdlhandle);
    exit(0);
}