何时在 C++ 中使用 extern "C"？
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When to use extern "C" in C++?
提问by pankajt
Possible Duplicate:
Why do we need extern “C”{ #include <foo.h> } in C++?
I have often seen programs coded like:
我经常看到程序编码如下：
extern "C" bool doSomeWork() {
//
return true;
}
Why do we use an extern "C"block? Can we replace this with something in C++? Is there any advantage to using extern "C"?
我们为什么要使用extern "C"块？我们可以用 C++ 中的东西替换它吗？使用有什么好处extern "C"吗？
I do see a link explaining thisbut why do we need to compile something in C when we already have C++?
我确实看到了一个解释这一点的链接，但是当我们已经有了 C++ 时，为什么我们需要用 C 编译一些东西？
回答by Artyom
extern "C" makes names not mangled.
extern "C" 使名称不被破坏。
It used when:
它在以下情况下使用：
We need to use some C library in C++
extern "C" int foo(int);We need export some C++ code to C
extern "C" int foo(int) { something; }We need an ability to resolve symbol in shared library -- so we need to get rid mangling
extern "C" int foo(int) { something; } /// typedef int (*foo_type)(int); foo_type f = (foo_type)dlsym(handle,"foo")
我们需要在 C++ 中使用一些 C 库
extern "C" int foo(int);我们需要将一些 C++ 代码导出到 C
extern "C" int foo(int) { something; }我们需要能够解析共享库中的符号——所以我们需要摆脱 mangling
extern "C" int foo(int) { something; } /// typedef int (*foo_type)(int); foo_type f = (foo_type)dlsym(handle,"foo")
回答by Cygon
One place where extern "C" makes sense is when you're linking to a library that was compiled as C code.
extern "C" 有意义的一个地方是当您链接到编译为 C 代码的库时。
extern "C" {
#include "c_only_header.h"
}
Otherwise, you might get linker errors because the library contains the functions with C-linkage (_myfunc) but the C++ compiler, which processed the library's header as C++ code, generated C++ symbol names for the functions ("_myfunc@XAZZYE" - this is called mangling and different for each compiler).
否则，您可能会收到链接器错误，因为该库包含带有 C-linkage (_myfunc) 的函数，但 C++ 编译器将库的标头作为 C++ 代码处理，生成函数的 C++ 符号名称（“_myfunc@XAZZYE” - 这是称为 mangling 并且每个编译器都不同）。
Another place where extern "C" is used is to guarantee C linkage even for functions written in C++, eg.
另一个使用 extern "C" 的地方是保证 C 链接，即使对于用 C++ 编写的函数，例如。
extern "C" void __stdcall PrintHello() {
cout << "Hello World" << endl;
}
Such a function can be exported to a DLL and will then be callable from other programming language because the compile will not mangle its name. If you added another overload of the same function, eg.
这样的函数可以导出到 DLL，然后可以从其他编程语言调用，因为编译不会破坏它的名称。如果您添加了相同功能的另一个重载，例如。
extern "C" void __stdcall PrintHello() {
cout << "Hello World" << endl;
}
extern "C" void __stdcall PrintHello(const char *name) {
cout << "Hello, " << name << endl;
}
Most compilers would then catch this and thus prevent you from using function overloads in your DLL-public functions.
大多数编译器会捕捉到这一点，从而阻止您在 DLL 公共函数中使用函数重载。
