动态库找不到main中定义的工厂
Dynamic Library cannot find the factory defined in main
我正在尝试实现用于在动态加载的库中填充工厂的代码。这里的代码示例来自here.
Shape.h（基础Class）
#ifndef __SHAPE_H
#define __SHAPE_H
#include <map>
#include <string>
using namespace std;
// base class for all shapes
class shape
{
public:
virtual void draw()=0;
};
// typedef to make it easier to set up our factory
typedef shape *maker_t();
// our global factory
extern map<string, maker_t *,less<string> > factory;
#endif // __SHAPE_H
Circle.h
#ifndef __CIRCLE_H
#define __CIRCLE_H
#include "Shape.h"
class circle : public shape
{
public:
void draw();
};
#endif // __CIRCLE_H
Circle.cpp
#include <iostream>
#include "Circle.h"
using namespace std;
void circle::draw()
{
// simple ascii circle<\n>
cout << "\n";
cout << " ****\n";
cout << " * *\n";
cout << " * *\n";
cout << " * *\n";
cout << " * *\n";
cout << " * *\n";
cout << " ****\n";
cout << "\n";
}
extern "C" {
shape *maker()
{
return new circle;
}
class proxy
{
public:
proxy()
{
// register the maker with the factory
factory["circle"] = maker;
}
};
// our one instance of the proxy
proxy p;
}
主要
#include <iostream>
#include <map>
#include <list>
#include <vector>
#include <string>
#include <dlfcn.h>
#include <stdio.h>
#include <unistd.h>
#include <string.h>
#include "Shape.h"
using namespace std;
// size of buffer for reading in directory entries
static unsigned int BUF_SIZE = 1024;
// our global factory for making shapes
map<string, maker_t *, less<string> > factory;
int main(int argc, char **argv)
{
FILE *dl; // handle to read directory
char *command_str = "ls *.so"; // command string to get dynamic lib names
char in_buf[BUF_SIZE]; // input buffer for lib names
list<void *> dl_list; // list to hold handles for dynamic libs
list<void *>::iterator itr;
vector<string> shape_names; // vector of shape types used to build menu
list<shape *> shape_list; // list of shape objects we create
list<shape *>::iterator sitr;
map<string, maker_t *, less<string> >::iterator fitr;
// get the names of all the dynamic libs (.so files) in the current dir
dl = popen(command_str, "r");
if (!dl)
{
perror("popen");
return(-1);
}
void *dlib;
char name[1024];
while (fgets(in_buf, BUF_SIZE, dl))
{
// trim off the whitespace
char *ws = strpbrk(in_buf, " \t\n");
if(ws)
{
*ws = '[=13=]';
}
// append ./ to the front of the lib name
sprintf(name, "./%s", in_buf);
dlib = dlopen(name, RTLD_NOW);
if(dlib == NULL)
{
cerr << dlerror() << endl;
return(-1);
}
// add the handle to our list
dl_list.insert(dl_list.end(), dlib);
}
int i = 0;
// create an array of the shape names
for (fitr=factory.begin(); fitr!=factory.end(); fitr++)
{
shape_names.insert(shape_names.end(), fitr->first);
i++;
}
int choice;
// create a menu of possible shapes to create and let the user make some
while (1)
{
i = 1;
for(fitr=factory.begin(); fitr!=factory.end(); fitr++)
{
cout << i << " - Create " << fitr->first << endl;
i++;
}
cout << i << " - Draw created shapes\n";
i++;
cout << i << " - Exit\n";
cout << "> ";
cin >> choice;
if (choice == i)
{
// destroy any shapes we created
for(sitr=shape_list.begin(); sitr!=shape_list.end(); sitr++)
{
delete *sitr;
}
// close all the dynamic libs we opened
for (itr=dl_list.begin(); itr!=dl_list.end(); itr++)
{
dlclose(*itr);
}
return(1);
}
if (choice == i - 1)
{
// draw the shapes
for (sitr=shape_list.begin(); sitr!=shape_list.end(); sitr++)
{
(*sitr)->draw();
}
}
if (choice > 0 && choice < i - 1)
{
// add the appropriate shape to the shape list
shape_list.insert(shape_list.end(), factory[shape_names[choice-1]]());
}
}
}
当我 运行 它时，出现以下错误：
./libCircle.so: undefined symbol: factory
怎样才能libCircle.so看到厂图并更新？
您的问题是默认情况下不导出可执行文件中的符号，因此对于 dlopen 加载的库无法解析。
来自 GNU ld 的手册：
-E
--export-dynamic
--no-export-dynamic
When creating a dynamically linked executable, using the -E option or
the --export-dynamic option causes the linker to add all symbols to the
dynamic symbol table. The dynamic symbol table is the set of symbols
which are visible from dynamic objects at run time.
If you do not use either of these options (or use the
--no-export-dynamic option to restore the default behavior), the
dynamic symbol table will normally contain only those symbols which are
referenced by some dynamic object mentioned in the link.
If you use "dlopen" to load a dynamic object which needs to refer back
to the symbols defined by the program, rather than some other dynamic
object, then you will probably need to use this option when linking the
program itself.
You can also use the dynamic list to control what symbols should be
added to the dynamic symbol table if the output format supports it.
See the description of --dynamic-list.
Note that this option is specific to ELF targeted ports. PE targets
support a similar function to export all symbols from a DLL or EXE; see
the description of --export-all-symbols below.
所以你的解决方案是：
- link 针对使用应导出符号的存根共享对象（请参阅“ 被 link 中提到的某些动态对象引用" 手册页中的文本）
- 将共享符号移动到一个单独的共享对象中，可执行文件和
dlopen'd 库都可以（动态地）link
- 在 link 时使用
--dynamic-list 从可执行文件中显式导出 factory
- 在 link 时间使用
--export-dynamic 从可执行文件中显式导出 所有 符号
您在 main.cpp 中定义了 "C++" 符号 factory，但是，您在其他文件中引用了 "C" 符号 "factory"。您还必须在 main.cpp 中使 factory 成为外部 "C"。
我正在尝试实现用于在动态加载的库中填充工厂的代码。这里的代码示例来自here.
Shape.h（基础Class）
#ifndef __SHAPE_H
#define __SHAPE_H
#include <map>
#include <string>
using namespace std;
// base class for all shapes
class shape
{
public:
virtual void draw()=0;
};
// typedef to make it easier to set up our factory
typedef shape *maker_t();
// our global factory
extern map<string, maker_t *,less<string> > factory;
#endif // __SHAPE_H
Circle.h
#ifndef __CIRCLE_H
#define __CIRCLE_H
#include "Shape.h"
class circle : public shape
{
public:
void draw();
};
#endif // __CIRCLE_H
Circle.cpp
#include <iostream>
#include "Circle.h"
using namespace std;
void circle::draw()
{
// simple ascii circle<\n>
cout << "\n";
cout << " ****\n";
cout << " * *\n";
cout << " * *\n";
cout << " * *\n";
cout << " * *\n";
cout << " * *\n";
cout << " ****\n";
cout << "\n";
}
extern "C" {
shape *maker()
{
return new circle;
}
class proxy
{
public:
proxy()
{
// register the maker with the factory
factory["circle"] = maker;
}
};
// our one instance of the proxy
proxy p;
}
主要
#include <iostream>
#include <map>
#include <list>
#include <vector>
#include <string>
#include <dlfcn.h>
#include <stdio.h>
#include <unistd.h>
#include <string.h>
#include "Shape.h"
using namespace std;
// size of buffer for reading in directory entries
static unsigned int BUF_SIZE = 1024;
// our global factory for making shapes
map<string, maker_t *, less<string> > factory;
int main(int argc, char **argv)
{
FILE *dl; // handle to read directory
char *command_str = "ls *.so"; // command string to get dynamic lib names
char in_buf[BUF_SIZE]; // input buffer for lib names
list<void *> dl_list; // list to hold handles for dynamic libs
list<void *>::iterator itr;
vector<string> shape_names; // vector of shape types used to build menu
list<shape *> shape_list; // list of shape objects we create
list<shape *>::iterator sitr;
map<string, maker_t *, less<string> >::iterator fitr;
// get the names of all the dynamic libs (.so files) in the current dir
dl = popen(command_str, "r");
if (!dl)
{
perror("popen");
return(-1);
}
void *dlib;
char name[1024];
while (fgets(in_buf, BUF_SIZE, dl))
{
// trim off the whitespace
char *ws = strpbrk(in_buf, " \t\n");
if(ws)
{
*ws = '[=13=]';
}
// append ./ to the front of the lib name
sprintf(name, "./%s", in_buf);
dlib = dlopen(name, RTLD_NOW);
if(dlib == NULL)
{
cerr << dlerror() << endl;
return(-1);
}
// add the handle to our list
dl_list.insert(dl_list.end(), dlib);
}
int i = 0;
// create an array of the shape names
for (fitr=factory.begin(); fitr!=factory.end(); fitr++)
{
shape_names.insert(shape_names.end(), fitr->first);
i++;
}
int choice;
// create a menu of possible shapes to create and let the user make some
while (1)
{
i = 1;
for(fitr=factory.begin(); fitr!=factory.end(); fitr++)
{
cout << i << " - Create " << fitr->first << endl;
i++;
}
cout << i << " - Draw created shapes\n";
i++;
cout << i << " - Exit\n";
cout << "> ";
cin >> choice;
if (choice == i)
{
// destroy any shapes we created
for(sitr=shape_list.begin(); sitr!=shape_list.end(); sitr++)
{
delete *sitr;
}
// close all the dynamic libs we opened
for (itr=dl_list.begin(); itr!=dl_list.end(); itr++)
{
dlclose(*itr);
}
return(1);
}
if (choice == i - 1)
{
// draw the shapes
for (sitr=shape_list.begin(); sitr!=shape_list.end(); sitr++)
{
(*sitr)->draw();
}
}
if (choice > 0 && choice < i - 1)
{
// add the appropriate shape to the shape list
shape_list.insert(shape_list.end(), factory[shape_names[choice-1]]());
}
}
}
当我 运行 它时，出现以下错误：
./libCircle.so: undefined symbol: factory
怎样才能libCircle.so看到厂图并更新？
您的问题是默认情况下不导出可执行文件中的符号，因此对于 dlopen 加载的库无法解析。
来自 GNU ld 的手册：
-E
--export-dynamic
--no-export-dynamic
When creating a dynamically linked executable, using the -E option or
the --export-dynamic option causes the linker to add all symbols to the
dynamic symbol table. The dynamic symbol table is the set of symbols
which are visible from dynamic objects at run time.
If you do not use either of these options (or use the
--no-export-dynamic option to restore the default behavior), the
dynamic symbol table will normally contain only those symbols which are
referenced by some dynamic object mentioned in the link.
If you use "dlopen" to load a dynamic object which needs to refer back
to the symbols defined by the program, rather than some other dynamic
object, then you will probably need to use this option when linking the
program itself.
You can also use the dynamic list to control what symbols should be
added to the dynamic symbol table if the output format supports it.
See the description of --dynamic-list.
Note that this option is specific to ELF targeted ports. PE targets
support a similar function to export all symbols from a DLL or EXE; see
the description of --export-all-symbols below.
所以你的解决方案是：
- link 针对使用应导出符号的存根共享对象（请参阅“ 被 link 中提到的某些动态对象引用" 手册页中的文本）
- 将共享符号移动到一个单独的共享对象中，可执行文件和
dlopen'd 库都可以（动态地）link - 在 link 时使用
--dynamic-list 从可执行文件中显式导出 - 在 link 时间使用
--export-dynamic 从可执行文件中显式导出 所有 符号
factory
您在 main.cpp 中定义了 "C++" 符号 factory，但是，您在其他文件中引用了 "C" 符号 "factory"。您还必须在 main.cpp 中使 factory 成为外部 "C"。