如何将DLL链接到新项目

Question

Header.h

#pragma once
#include <string>
using namespace std;
#define DLLIMPORT __declspec(dllexport)
extern "C" {
DLLIMPORT class Config {
public:
static string path;
static string test;
static void get_file();
};
DLLIMPORT Config* GetConfigInstance();
}

dllmain.cpp

#include "pch.h"
#include "Header.h"
#include <iostream>
#include <fstream>
#include <direct.h>
BOOL APIENTRY DllMain(HMODULE hModule,
DWORD  ul_reason_for_call,
LPVOID lpReserved
)
{
switch (ul_reason_for_call)
{
case DLL_PROCESS_ATTACH:
case DLL_THREAD_ATTACH:
case DLL_THREAD_DETACH:
case DLL_PROCESS_DETACH:
break;
}
return TRUE;
}

string Config::path;
string Config::test;
void Config::get_file() {
ifstream infile("cfg.txt");
char cwd[1024];
if (_getcwd(cwd, sizeof(cwd)) == nullptr) {
std::cerr << "Failed to get current working directory" << std::endl;
}
std::cout << "Current working directory: " << cwd << std::endl;
std::cout << "Reading file: " << cwd << "/cfg.txt" << std::endl;
string line;
while (getline(infile, line)) {
size_t pos = line.find("=");
string key = line.substr(0, pos);
string val = line.substr(pos + 1);
if (key == "img_path") {
path = val;
}
else if (key == "test") {
test = val;
}
}
}
Config* GetConfigInstance()
{
return new Config();
}

main.cpp

#include <iostream>
#include <windows.h>
#include "Header.h"
int main() {
HINSTANCE hinstLib = LoadLibrary(TEXT("Util_aoi_model.dll"));
if (hinstLib == NULL) {
std::cerr << "Failed to load DLL" << std::endl;
return 1;
}
typedef Config* (*GetConfigInstanceFunction)();
GetConfigInstanceFunction getConfigInstance = (GetConfigInstanceFunction)GetProcAddress(hinstLib, "GetConfigInstance");
if (getConfigInstance == NULL) {
std::cerr << "Failed to get address of GetConfigInstance function" << std::endl;
return 1;
}
Config* config = getConfigInstance();
config->get_file();
std::cout << "img_path: " << Config::path << std::endl;
std::cout << "test: " << Config::test << std::endl;
FreeLibrary(hinstLib);
return 0;
}

我一直在构建.dll和.lib，但当我使用另一个.sln来调用它们时，它会显示错误：

未解析的外部符号

我确信我添加了include路径和lib路径。

链接输入具有.lib的名称。

有人能帮我纠正这个错误吗？

header.h和dllmain.cpp文件在同一个项目中，并构建一个.dll和.lib。

另一个main.cpp在一个新项目中，我正在尝试使用DLL函数get_file()。

Answer 1

您的方法不会像编写的那样工作。在第二个解决方案中，编译器正在寻找get_file()的实现，但它无法访问该实现。此外，您不能跨越DLL边界使用像std::string这样的非平凡类型。

您需要从Config中删除所有数据成员，并使其所有方法都是非静态的纯虚拟方法。换句话说，使Config成为一个抽象接口。然后让DLL使用一个单独的类来实现该接口，然后它可以实例化并返回一个指向该接口的指针

试试这个：

收割台.h

#pragma once
#ifdef BUILDING_DLL
#define DLLIMPORT __declspec(dllexport)
#else
#define DLLIMPORT __declspec(dllimport)
#endif
extern "C" {
class Config {
public:
virtual const char* get_path() = 0;
virtual const char* get_test() = 0;
virtual void get_file() = 0;
};
DLLIMPORT Config* GetConfigInstance();
}

dllmain.cpp

#include "pch.h"
#define BUILDING_DLL
#include "Header.h"
#include <iostream>
#include <fstream>
#include <string>
#include <direct.h>
using namespace std;
BOOL APIENTRY DllMain(HMODULE hModule,
DWORD  ul_reason_for_call,
LPVOID lpReserved
)
{
switch (ul_reason_for_call)
{
case DLL_PROCESS_ATTACH:
case DLL_THREAD_ATTACH:
case DLL_THREAD_DETACH:
case DLL_PROCESS_DETACH:
break;
}
return TRUE;
}
class ConfigImpl : public Config {
public:
string path;
string test;
const char* get_path() override;
const char* get_test() override;
void get_file() override;
};
const char* ConfigImpl::get_path() {
return path.c_str();
}
const char* ConfigImpl::get_test() {
return test.c_str();
}
void ConfigImpl::get_file() {
ifstream infile("cfg.txt");
char cwd[1024];
if (_getcwd(cwd, sizeof(cwd)) == nullptr) {
cerr << "Failed to get current working directory" << endl;
}
cout << "Current working directory: " << cwd << endl;
cout << "Reading file: " << cwd << "/cfg.txt" << endl;
string line;
while (getline(infile, line)) {
size_t pos = line.find("=");
string key = line.substr(0, pos);
string val = line.substr(pos + 1);
if (key == "img_path") {
path = val;
}
else if (key == "test") {
test = val;
}
}
}
Config* GetConfigInstance()
{
static ConfigImpl impl;
return &impl;
}

main.cpp

#include <iostream>
#include <windows.h>
#include "Header.h"
int main() {
HINSTANCE hinstLib = LoadLibrary(TEXT("Util_aoi_model.dll"));
if (hinstLib == NULL) {
std::cerr << "Failed to load DLL" << std::endl;
return 1;
}
typedef Config* (*GetConfigInstanceFunction)();
GetConfigInstanceFunction getConfigInstance = (GetConfigInstanceFunction)GetProcAddress(hinstLib, "GetConfigInstance");
if (getConfigInstance == NULL) {
std::cerr << "Failed to get address of GetConfigInstance function" << std::endl;
return 1;
}
Config* config = getConfigInstance();
config->get_file();
std::cout << "img_path: " << config->get_path() << std::endl;
std::cout << "test: " << config->get_test() << std::endl;
FreeLibrary(hinstLib);
return 0;
}