C++ 为什么我会收到符号查找错误？
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Why am I getting a symbol lookup error?
提问by S?my
I am writing a library, which is dynamically loaded in my main-application with dlsym. I have the following files:
我正在编写一个库，它使用 dlsym 动态加载到我的主应用程序中。我有以下文件：
library.h
图书馆.h
#include <ilibrary.h>
#include <igateway.h>
class LibraryImpl;
class Library: public ILibrary {
public:
static ILibrary* instance();
IGateway* getGateway() const;
protected:
Library();
virtual ~Library();
private:
static ILibrary* instance_;
LibraryImpl* library_;
};
extern "C" {
IMPORT_EXPORT ILibrary* getLibrary();
}
library.cpp
库文件
#include "library.h"
#include "business/BCGateway.h"
class LibraryImpl {
public:
IGateway* getGateway();
};
IGateway* LibraryImpl::getGateway() {
return BCGateway::instance();
}
ILibrary* Library::instance_ = NULL;
ILibrary* Library::instance() {
return instance_ ? instance_ : (instance_ = new Library);
}
Library::Library() {
library_ = new LibraryImpl();
}
Library::~Library() {
delete library_;
}
IGateway* Library::getGateway() const {
return library_->getGateway();
}
extern "C" {
IMPORT_EXPORT
ILibrary* getLibrary(){
return Library::instance();
}
}
business/BCGateway.h
商业/BCGateway.h
#include <igateway.h>
class BCGateway: public IGateway {
public:
static IGateway* instance();
protected:
BCGateway();
private:
static IGateway* instance_;
};
business/BCGateway.cpp
业务/BCGateway.cpp
#include "BCGateway.h"
IGateway* BCGateway::instance_ = NULL;
IGateway* BCGateway::instance(){
return instance_ ? instance_ : (instance_ = new BCGateway);
}
I can connect to the library and successfully load the Library-instance. But when I call library->getGateway() in my main-app I get the following error:
我可以连接到库并成功加载库实例。但是当我在主应用程序中调用 library->getGateway() 时，出现以下错误：
symbol lookup error: ./gateways/libSwisscomXtraZone.so: undefined symbol: _ZN9BCGateway8instanceEv
符号查找错误：./gateways/libSwisscomXtraZone.so：未定义符号：_ZN9BCGateway8instanceEv
Can you please give me a hint, how I can resolve this? I'm stuck.
你能给我一个提示，我该如何解决这个问题？我被困住了。
Thanks.
谢谢。
回答by Johannes Schaub - litb
I put the error through c++filt, it says that the mangled name stands for
我解决了错误c++filt，它说损坏的名称代表
BCGateway::instance()
This suggests that you call BCGateway::instance()somewhere and forgot to link against BCGateway.oor you even forgot to define BCGateway::instance().
这表明您在BCGateway::instance()某处调用并忘记链接，BCGateway.o或者您甚至忘记定义BCGateway::instance().
回答by Goz
well all static members must be intialised in a cpp file. Seeing as BCGateway::instance is not intialised at any point it will be unable to find the symbol. The problem is, however, that if you create a BCGateway.cpp and initialise the instance then you will end up only having one instance across, potentially, many processes. This may or may not be a problem depending on how you use the DLL.
好吧，所有静态成员都必须在 cpp 文件中初始化。看到 BCGateway::instance 在任何时候都没有初始化，它将无法找到符号。然而，问题是，如果您创建一个 BCGateway.cpp 并初始化该实例，那么您最终只会拥有一个跨多个进程的实例。这可能是也可能不是问题，具体取决于您使用 DLL 的方式。
