c库没有使用gcc/g++链接

I have a c-library which I use in gcc. The library has the extension .lib but is always linked as a static library. If i write a program which uses the library as c-code, everything as a-ok. If I however rename the file to .cpp (doing simple stuff that works in both c/c++) I get undefined reference. These are simple small programs I write for testing purposes so no fancy stuff. I compile using:

我有一个c库，我用在gcc中。该库具有扩展名.lib，但总是以静态库的形式链接。如果我写一个程序用库作为c-code，一切都是a-ok。但是，如果我将文件重命名为.cpp(做一些简单的工作，可以在c/c++中工作)，我将得到未定义的引用。这些是我为测试目的编写的简单的小程序，所以没有什么花哨的东西。我编译使用:

gcc -g -Wall -I <path to custom headers> -o program main.c customlibrary.lib -lm -lpthread

The above works like a charm. However:

上面的作品很有魅力。然而:

g++ -g -Wall -I <path to custom headers> -o program main.cpp customlibrary.lib -lm -lpthread

或

gcc -g -Wall -I <path to custom headers> -o program main.cpp customlibrary.lib -lm -lpthread -lstdc++

results in undefined reference to any function in customlibrary.lib. I tried creating a symbolic link named customlibrary.a but no luck.

结果在自定义库中对任何函数的未定义引用。我尝试创建一个名为customlibrary的符号链接。但没有运气。

Why won't g++ find recognize my library. Unfortunately I have no access to the source code of the libraries but linking a c-lib to c++ should not be a problem right?

为什么g++找不到我的图书馆?不幸的是，我无法访问库的源代码，但是将c-lib链接到c++应该不是问题，对吗?

3 个解决方案

#1

Your library appears to have an API that assumes it will be called from C, not C++. This is important because C++ effectively requires that the symbols exported from a library have more information in them than just the function name. This is handled by "name mangling" the functions.

您的库似乎有一个API，它假定将从C而不是c++调用它。这很重要，因为c++有效地要求从库导出的符号中包含的信息要比函数名更多。这是通过“名称管理”函数来处理的。

I assume your library has an include file that declares its public interface. To make it compatible with both C and C++, you should arrange to tell a C++ compiler that the functions it declares should be assumed to use C's linkage and naming.

我假设您的库有一个包含文件，该文件声明了它的公共接口。为了使它与C和c++兼容，您应该安排告诉c++编译器，它声明的函数应该假定使用C的链接和命名。

A likely easy answer to test this is to do this:

一个很容易测试的答案是:

extern "C" {
#include "customlibrary.h"
}

in your main.cpp instead of just including customlibrary.h directly.

在你的主。cpp而不是仅仅包含customlibrary。直接h。

To make the header itself work in both languages and correctly declare its functions as C-like to C++, put the following near the top of the header file:

要使头文件本身在两种语言中工作，并正确地将其功能声明为C-like到c++，请将以下内容放在头文件的顶部附近:

#ifdef __cplusplus
extern "C" {
#endif

and the following near the bottom:

下面是下面的内容:

#ifdef __cplusplus
}
#endif

#2

The C++ compiler performs what is known as name-mangling - the names that appear in your code are not the same ones as your linker sees. The normal way round this is to tell the compiler that certain functions need C linkage:

c++编译器执行所谓的名称管理——代码中出现的名称与链接器看到的名称不同。通常的方法是告诉编译器某些函数需要C连接:

// myfile.cpp
extern "C" int libfun();    // C function in your library

or do it for a whole header file:

或者对整个头文件这样做:

// myfile.cpp
extern "C" {
  #include "mylibdefs.h"      // defs for your C library functions
}

#3

Does your header file have the usual

你的头文件有通常的吗

#ifdef __cplusplus
extern "C" {
#endif

// ...

#ifdef __cplusplus
} /* extern "C" */
#endif

to give the library functions C linkage explicitly.

要显式地给库函数C链接。

.cpp files are compiled with C++ linkage i.e. name mangling by default.

.cpp文件使用c++链接进行编译，即默认名称管理。

#1