如何从masm引用外部C ++函数? [英] how do I reference an external C++ function from masm?

问题描述

我目前正在学习masm，但是在调用外部函数时遇到问题.

I'm currently learning masm and I am having a problem calling an external function.

我在c ++中有一个称为writei的函数，它接收一个uint64并将其输出.

I have a function in c++ which is called writei, it receives a uint64 and outputs it.

int writei(uint64_t a)
{
    cout << a;
    return 1;
}

我尝试从.asm文件中提取"并调用它，但是编译器抛出在函数mai中引用的未解析的外部符号writei".

I tried "extrn"ing and calling it from an .asm file but the compiler throws "unresolved external symbol writei referenced in function mai".

这是masm代码(我正在使用Visual Studio 2019)

this is the masm code (I'm using visual studio 2019)

extern writei : proto


.code
mai proc
    push rbp
    push rsp
    mov ecx,3
    call writei
    pop rsp
    pop rbp
    ret
mai endp
end

推荐答案

除其他事项外，您还需要.

Among other things, you need "extern C" in your C++ method declaration.

例如:

extern "C" {
  int writei(uint64_t a);
}

int writei(uint64_t a)
{
    cout << a;
    return 1;
}

这是一篇很好的文章，详细介绍了这一点:

Here's a good article that explains this in more detail:

ISO C ++常见问题解答:如何混合使用C和C ++

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