将 C 库用于 C++ 程序
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Using C Libraries for C++ Programs
提问by johngreen
I am trying to control Dynamixel servos using a GUI made using Qt. Dynamixel provides a C set of C librariesto control the motors, while the only way of making GUI's I know is Qt, which is essentially C++. Will it be possible to use Dynamixel C libraries from Qt C++ code in any way?
我正在尝试使用使用 Qt 制作的 GUI 来控制 Dynamixel 伺服系统。Dynamixel 提供了一组C 库来控制电机，而我知道制作 GUI 的唯一方法是 Qt，它本质上是 C++。是否可以以任何方式使用 Qt C++ 代码中的 Dynamixel C 库？
回答by André Oriani
Yes, C++ can compile C with a C++ compiler and you can link C++ against C. Just be sure that any C function you call uses C linkage. This is made by enclosing the prototype of the C function by an extern "C"
是的，C++ 可以使用 C++ 编译器编译 C，并且您可以将 C++ 与 C 链接。只要确保您调用的任何 C 函数都使用 C 链接。这是通过将 C 函数的原型包含在一个extern "C"
#ifdef __cplusplus
extern "C"{
#endif
void c_function_prototype();
#ifdef __cplusplus
}
#endif
The headers for the library you are trying to use may already do that.
您尝试使用的库的标头可能已经这样做了。
回答by Jason
Sure ... C code is called from C++ all the time. For instance, most OS libraries are written in C rather than C++. So whenever you're making syscalls from your C++ code to perform tasks that are handed over to the OS kernel, those are going through C-code calls.
当然...... C 代码总是从 C++ 调用。例如，大多数操作系统库是用 C 编写的，而不是 C++。因此，每当您从 C++ 代码进行系统调用以执行移交给操作系统内核的任务时，这些都是通过 C 代码调用进行的。
Just be sure to include the proper headers and link against the C-libraries in question at compile time. Also remember to use extern "C"to specify C-linkage for the C-library functions if the header files have not already declared them as such. Keep in mind that some libraries may not have declared their functions specifically using extern "C", but may have used a pre-processor token to-do so. So you'll want to check for that as well before you assume the library writers did not already define their library as having C-linkage.
只要确保在编译时包含正确的头文件并链接到有问题的 C 库。extern "C"如果头文件还没有这样声明它们，还记得使用为 C 库函数指定 C 链接。请记住，某些库可能没有专门使用 声明它们的函数extern "C"，但可能使用了预处理器令牌来这样做。因此，在您假设库编写者尚未将其库定义为具有 C 链接之前，您还需要检查一下。
linking custom libraries using gcccan be done with the -lswitch. If you need to specify a custom directory for where the libraries are located, that can be done with the -Lswitch. So for instance:
gcc可以使用-lswitch来链接自定义库。如果您需要为库所在的位置指定自定义目录，则可以使用-Lswitch来完成。所以例如：
g++ -std=c++11 my_code.cpp -lmy_library -L/custom_directory_path
Note that the -land -Lswitches come afterthe code or object files you're compiling, and if you're library is something like libjpg, or librobotics, etc., drop the libpart of the name when you append it to the -lswitch.
请注意，-l和-L开关来后，你编译代码或目标文件，如果你的库是一样的东西libjpg，或者librobotics，等放下lib，当你把它添加到名称的一部分-l开关。
回答by Jason
Yes. To use C library function use extern "C" as below in your .cpp program , myprog.cpp
是的。要使用 C 库函数，请在 .cpp 程序 myprog.cpp 中使用如下所示的 extern "C"
extern "C" {
// C Function call
cfunc();
}
int main()
{
cfunc();
return 0;
}
This cfunc should be defined in c library as below prog.c
这个 cfunc 应该在 c 库中定义如下 prog.c
#include <stdio.h>
void cfunc()
{
printf("This is from c library");
}
Then you need to create .oobject file and .soshared object files for your C library as below
然后你需要为你的 C 库创建.o目标文件和.so共享目标文件，如下所示
$] gcc -c prog.c -o prog
$] gcc -shared -o libprog.so prog.o
$] export LD_LIBRARY_PATH=/path/to/clibrary:$LD_LIBRARY_PATH
$] g++ -L/path/to/clibrary myprog.cpp -o myprog.o -lprog
回答by Michael Anderson
You can use C libraries from C++... however there are some caveats.
您可以使用 C++ 中的 C 库...但是有一些注意事项。
One big thing to watch out when using third-party C libraries with C++ is error handling.
将第三方 C 库与 C++ 一起使用时需要注意的一件大事是错误处理。
Some C libraries use facilities like setjmp/longjmpfor error handling. (lua is a notable example). This means that on error stack unwinding will not occur in the normal manner, and you may leak resources. Things like the usual C++ RAII style guards for resource protection fail dismally. (These calls are worse than gotofor C++ code).
一些 C 库使用setjmp/ 之类的工具longjmp进行错误处理。（lua 是一个显着的例子）。这意味着错误堆栈展开不会以正常方式发生，并且您可能会泄漏资源。像通常用于资源保护的 C++ RAII 风格的守卫之类的东西失败了。（这些调用比gotoC++ 代码更糟糕）。
Also exceptions can be a concern. If a C++ exception propagates to a C/C++ boundary then the application may terminate rather than propagating the exception. (Depending on how the C library was compiled and your OS etc.) (You might get this situation if you pass a C++ function into a C library as a callback.)
异常也可能是一个问题。如果 C++ 异常传播到 C/C++ 边界，则应用程序可能会终止而不是传播异常。（取决于 C 库的编译方式和您的操作系统等）（如果您将 C++ 函数作为回调传递给 C 库，您可能会遇到这种情况。）
回答by ssgreg
Dont forget about extern "C"around the library headers.
Read here. How does C's "extern" work?
不要忘记extern "C"围绕库标题。在这里阅读。C的“外部”如何工作？
回答by Adrian Cornish
Yes - C++ can use C libraries.
是的 - C++ 可以使用 C 库。
This is an example that uses libc the main C library
这是一个使用 libc 主 C 库的示例
#include <cstdio>
int main()
{
printf("%s\n", "Hello world");
return 0;
}
回答by Jakob
There is a C++ driverfor Dynamixel servos in the Rock Framework.
Rock Framework 中有一个用于 Dynamixel 舵机的C++ 驱动程序。
