静态库&动态库&导入库
我遇到的问题
先贴一个StackOverflow上的问题
上面的问题让我知道了更多动态库的知识。
我需要使用一个声音库(irrKlang)为2d游戏提供声音，我使用的编译器是mingw-w64，但是irrKlang只为windows提供了msvc的动态库，不同编译器产生的库往往不能同时调用，我在链接库时发生了问题。因为不用编译器对c++函数的命名方式不同，msvc命名尤其混乱，导致由于符号不对应无法成功链接。
c库就没有这些蛋疼的问题，由于没有重载啥的，c的函数名就是最后的符号名
我的问题不能通过自己生成导入库解决，因为没法变符号命名约定，像下面这样：
函数声明：
ISoundEngine* createIrrKlangDevice(E_SOUND_OUTPUT_DRIVER driver,int options,const char*,const char*);
gcc的命名方式:
__imp__ZN8irrklang20createIrrKlangDeviceENS_21E_SOUND_OUTPUT_DRIVEREiPKcS2_
msvc的命名方式：
?createIrrKlangDevice@irrklang@@YAPEAVISoundEngine@1@W4E_SOUND_OUTPUT_DRIVER@1@HPEBD1@Z
我的解决思路是直接通过符号查找函数地址：
linux上从库中查找函数需要这些：
#include <dlfcn.h>
void *dlopen(const char *filename, int flag);
char *dlerror(void);
void *dlsym(void *handle, const char *symbol); // 腾讯的libco中就是用这个函数hook了系统调用
int dlclose(void *handle);
windows下:
#include <windows.h>
HMODULE LoadLibrary(LPCSTR lpLibFileName); // LoadLibraryW（Unicode）和LoadLibraryA（ANSI）
FARPROC GetProcAddress(HMODULE hModule, LPCSTR lpProcName);
BOOL FreeLibrary(HMODULE hLibModule);
我用符号成功找到了函数指针，也成功调用了，但是由于不了解irrklang内部，播放音乐的时候崩了，这个问题解决失败了。
我在StackOverflow上发起了一个提问
静态库(static library)动态库(dynamic library)导入库(import library)
引用一下learncpp.com的相关介绍
A static library (also known as an archive) consists of routines that are compiled and linked directly into your program. When you compile a program that uses a static library, all the functionality of the static library that your program uses becomes part of your executable. On Windows, static libraries typically have a .lib extension, whereas on linux, static libraries typically have an .a (archive) extension. One advantage of static libraries is that you only have to distribute the executable in order for users to run your program. Because the library becomes part of your program, this ensures that the right version of the library is always used with your program. Also, because static libraries become part of your program, you can use them just like functionality you’ve written for your own program. On the downside, because a copy of the library becomes part of every executable that uses it, this can cause a lot of wasted space. Static libraries also can not be upgraded easy -- to update the library, the entire executable needs to be replaced.
A dynamic library (also called a shared library) consists of routines that are loaded into your application at run time. When you compile a program that uses a dynamic library, the library does not become part of your executable -- it remains as a separate unit. On Windows, dynamic libraries typically have a .dll (dynamic link library) extension, whereas on Linux, dynamic libraries typically have a .so (shared object) extension. One advantage of dynamic libraries is that many programs can share one copy, which saves space. Perhaps a bigger advantage is that the dynamic library can be upgraded to a newer version without replacing all of the executables that use it.
Because dynamic libraries are not linked into your program, programs using dynamic libraries must explicitly load and interface with the dynamic library. This mechanism can be confusing, and makes interfacing with a dynamic library awkward. To make dynamic libraries easier to use, an import library can be used.
An import library is a library that automates the process of loading and using a dynamic library. On Windows, this is typically done via a small static library (.lib) of the same name as the dynamic library (.dll). The static library is linked into the program at compile time, and then the functionality of the dynamic library can effectively be used as if it were a static library. On Linux, the shared object (.so) file doubles as both a dynamic library and an import library. Most linkers can build an import library for a dynamic library when the dynamic library is created.
静态库：后缀名win:.lib linux:.a, 直接链接到程序中
动态库：后缀名win:.dll linux:.so, 不会成为可执行文件的一部分。两种加载方式：1.隐式加载：将导入库想静态库一样链接 2.通过系统提供的api运行时加载
导入库：后缀名win:.lib, 使加载和使用动态库的过程自动化。linux上.so文件既是动态库又是导入库。导入库中不含代码，而是为链接程序提供信息，包含建立动态链接时要用到的重定位表。
使用mingw-w64的工具为动态链接库生成导入库
windows的.dll(msvc生成的)通常不能直接链接到gcc编译的程序，要为它生成导入库
> gendef.exe foo.dll # 生成导出定义，这个文件包含导出的函数符号
> dlltool.exe --dllname foo.dll --input-def foo.def --output-lib libfoo.lib # 生成导入库
# 只有msvs也就是win的动态库需要生成导入库，对gcc生成的动态库执行会失败
> gendef.exe glfw3.dll
* [glfw3.dll] Found PE+ image
* failed to create glfw3.def ...
# 猜测 pe+ 格式的动态库可能包含导入库(想linux的.so一样)， 只有不是pe+格式才需要导入库
