“void function()"和“void function()"有什么区别?和“void *function()"? [英] What is the difference between "void function()" and "void *function()"?

问题描述

我知道 void *function() 是指向函数的指针，但我不知道它们的工作方式以及何时使用 void *function()代码>?我在组装方面做了一些研究，以比较它们在幕后的工作方式以及它们看起来是一样的.这是 C++ 代码:

I knew the void *function() is the pointer which point to a function but I don't know how different they work and when we use void *function()? I did some research in assembly to compare how they work behind the scene and look like they are same. Here is the c++ code:

void *bar(){
        std::cout << "bar" << std::endl;
}

void foo(){
        std::cout << "foo" << std::endl;
}

int main(void){
        foo();
        bar();

        return 0;
}

这是我从 objdump 收到的汇编指令

And this is assembly instruction I receive from objdump

void *bar(){
  400846:       55                      push   %rbp
  400847:       48 89 e5                mov    %rsp,%rbp
        std::cout << "bar" << std::endl;
  40084a:       be 84 09 40 00          mov    $0x400984,%esi
  40084f:       bf 60 10 60 00          mov    $0x601060,%edi
  400854:       e8 b7 fe ff ff          callq  400710 <_ZStlsISt11char_traitsIcEERSt13basic_ostreamIcT_ES5_PKc@plt>
  400859:       be 30 07 40 00          mov    $0x400730,%esi
  40085e:       48 89 c7                mov    %rax,%rdi
  400861:       e8 ba fe ff ff          callq  400720 <_ZNSolsEPFRSoS_E@plt>
}
  400866:       90                      nop
  400867:       5d                      pop    %rbp
  400868:       c3                      retq   

0000000000400869 <_Z3foov>:

void foo(){
  400869:       55                      push   %rbp
  40086a:       48 89 e5                mov    %rsp,%rbp
        std::cout << "foo" << std::endl;
  40086d:       be 88 09 40 00          mov    $0x400988,%esi
  400872:       bf 60 10 60 00          mov    $0x601060,%edi
  400877:       e8 94 fe ff ff          callq  400710 <_ZStlsISt11char_traitsIcEERSt13basic_ostreamIcT_ES5_PKc@plt>
  40087c:       be 30 07 40 00          mov    $0x400730,%esi
  400881:       48 89 c7                mov    %rax,%rdi
  400884:       e8 97 fe ff ff          callq  400720 <_ZNSolsEPFRSoS_E@plt>
}
  400889:       90                      nop
  40088a:       5d                      pop    %rbp
  40088b:       c3                      retq   

000000000040088c <main>:

int main(void){
  40088c:       55                      push   %rbp
  40088d:       48 89 e5                mov    %rsp,%rbp
        foo();
  400890:       e8 d4 ff ff ff          callq  400869 <_Z3foov>
        bar();
  400895:       e8 ac ff ff ff          callq  400846 <_Z3barv>

        return 0;
  40089a:       b8 00 00 00 00          mov    $0x0,%eax
}
  40089f:       5d                      pop    %rbp
  4008a0:       c3                      retq   

推荐答案

重复你在评论中的答案，区别在于返回的类型

To repeat the answers you had in the comments already, the difference is the type returned

void foo() { ... }

是一个什么都不返回的函数，而

Is a function that returns nothing, while

void *bar() { ... }
void* bar() { ... } // Identical

返回一个 void 指针.在 * 之前或之后交换空格位置在这里没有区别，但它可能会使返回类型更清楚.当然，在这个 bar 函数的情况下，当然要确保实际返回一些东西，否则你至少会收到编译器警告和未定义的行为.

Return a void pointer. Swapping the space position before or after the * makes no difference here, but it may make it clearer what the return type is. And of course make sure to actually return something in the case of this bar function, or you will have a compiler warning at least, and undefined behavior.

所以基本上这只是要记住的关键字 void 的两个略有不同的含义.如果您不熟悉 C++，这里有大量可访问的书籍也可以帮助您.

So basically this is just two slightly different meanings of the keyword void to remember. If you are not familiar with C++ there a good amount of accessible book that can help you too.

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