从目标C调用C ++方法 [英] Calling C++ method from Objective C

问题描述

我有以下文件.

foo.h(C ++头文件)
foo.mm(C ++文件)
test_viewcontroller.h(目标c头文件)
test_viewcontroller.m(目标c文件)

foo.h (C++ header file)
foo.mm (C++ file)
test_viewcontroller.h (objective c header file)
test_viewcontroller.m (Objective c file)

我在foo.h中声明了一个donothing()方法并在foo.mm中定义了它.

I have declared a method donothing() in foo.h and defined it in foo.mm.Lets say it is

双牙(双a) { 返回 }

double donothing(double a) { return a; }

现在，我尝试在test_viewcontroller.m中调用此函数

Now,I try to call this function in test_viewcontroller.m

double var = donothing(somevar);

double var = donothing(somevar);

我在test_viewcontroller.o中收到链接器错误，提示找不到符号" _donothing().
collect2:ld返回了1个退出状态

I get linker error which says "cannot find symbols" _donothing() in test_viewcontroller.o
collect2: ld returned 1 exit status

有人可以指出什么错吗?

Can anyone please point me as to what is wrong?

让我说清楚:

#ifdef __cplusplus 

extern "C" 
{
      char UTMLetterDesignator(double Lat);
      NSString * LLtoUTM(double Lat,double Long,double UTMNorthing, double UTMEasting);
      double test(double a);
}

#endif

@卡尔

我已经包含了我的代码示例.是说我只需要将test()方法包装到ifdef中.我不知道它可以产生什么变化.您能解释一下吗?

I have included my code sample.Are saying that I need to wrap only the test() method in ifdef.I dont understand what difference it can make.Can you please explain?

推荐答案

test_viewcontroller.m正在寻找donothing()的非C ++混合符号名称.将其扩展名更改为.mm，您应该会很好.或者，在编译C ++文件时，将extern "C"声明放在foo.h中的方法声明上.

test_viewcontroller.m is looking for a non-C++-mangled symbol name for donothing(). Change its extension to .mm and you should be good. Alternately, put an extern "C" declaration on your method declaration in foo.h when compiling the C++ file.

您要使它看起来像这样:

You want to have it look like this:

foo.h:

#ifdef __cplusplus
extern "C" {
#endif

double donothing(double a);

#ifdef __cplusplus
}
#endif

foo.mm:

#include "foo.h"

double donothing(double a)
{
    return a;
}

test_viewcontroller.m:

test_viewcontroller.m:

#import "foo.h"

- (double)myObjectiveCMethod:(double)x
{
    return donothing(x);
}

这篇关于从目标C调用C ++方法的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！