在C中调用文件C ++函数 [英] Calling C++ functions from C file

问题描述

我很新的C和C ++。但我有一些C ++函数，我需要从C叫他们我做了什么，我需要做的例子

I am quite new to C and C++. But I have some C++ functions which I need to call them from C. I made an example of what I need to do

的的main.c 的：

#include "example.h"      
#include <stdio.h>

int main(){   
    helloWorld();
    return 0;
}

---

的 example.h文件的：

 #ifndef HEADER_FILE
 #define HEADER_FILE

 #ifdef __cplusplus
     extern "C" {
 #endif
         void helloWorld();
 #ifdef __cplusplus
     }
 #endif

 #endif

---

的 example.cpp 的：

#include <iostream.h>

void helloWorld(){
    printf("hello from CPP");
} 

---

这是行不通的。我还收到我的的main.c 未定义参考 _helloWorld 的错误。哪里的问题？

---

It just doesn't work. I still receive the error of undefined reference to _helloWorld in my main.c. Where is the the problem?

推荐答案

简短的回答：

example.cpp 应包括 example.h文件。

再回应：

当您在C ++中声明的函数，它有C ++联动和调用约定。 （实际上这是最重要的功能就是名称重整 - 由C ++编译器会改变一个符号的名称进程。这样就可以有在参数类型各不相同的同名函数）的externC（在你的头文件present）是围绕它自己的方式 - 它规定，这是一个C函数，从C code，如调用。未进行重整。

When you declare a function in C++, it has C++ linkage and calling conventions. (In practice the most important feature of this is name mangling - the process by which a C++ compiler alters the name of a symbol so that you can have functions with the same name that vary in parameter types.) extern "C" (present in your header file) is your way around it - it specifies that this is a C function, callable from C code, eg. not mangled.

您有的externC在你的头文件，这是一个良好的开端，但你的C ++文件没有包括它并没有为externC在声明中，所以它不知道编译它作为一个C函数。

You have extern "C" in your header file, which is a good start, but your C++ file is not including it and does not have extern "C" in the declaration, so it doesn't know to compile it as a C function.

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