C ++，为一个返回类型的函数创建一个pthread？ [英] C++, create a pthread for a function with a return type?

问题描述

说我有以下函数：

  bool foo（int a）; //此方法声明不能更改。 
  

如何创建一个pthread？我怎么知道函数返回了什么？我在网上看，似乎任何函数，我想创建一个pthread必须以 void * 作为参数，必须返回 void * 以及，我不太确定如何铸造所有这一切将工作，或在哪里我会得到返回的布尔。

我是C ++新手，请随身携带=）

解决方案>

只要你只处理bools（实际上是整数），有可能将函数转换为pthread函数类型，因为指针与（一些）整数是兼容的类型：

  pthread_t pid; 
 pthread_create（& pid，NULL，（void *（*）（void *））foo，（void *）argument）但是，你最好将函数包装到另一个与pthread兼容的函数中，然后返回一个指针，然后返回一个指针。到它的返回值（使用后必须是free（）'d）：
  void * foo_wrapper（void * arg）
 {
 int a = *（int *）arg; 
 bool retval = foo（a）; 
 bool * ret = malloc（sizeof（bool））; 
 * ret = retval; 
 return ret; 
} 
  
然后使用：
  pthread_t pid; 
 pthread_create（& pid，NULL，foo_wrapper，& a）; 
  
使用这种方法，以后你可以调用任意返回或参数类型。
 
Say I have the following function:
bool foo (int a); // This method declaration can not be changed.
How do I create a pthread for this? And how do I find out what the function returned? I've looked online and it seems like any function I want to create a pthread for must take a void* as an argument, and must return void* as well, and I'm not quite sure how the casting for all this would work, or where I would get the returned bool. 

I'm new to C++, so please bear with me =) 
解决方案
As far as you're dealing only with bools (which are, in fact, integers) it's possible, however not recommended, to cast the function to a pthread function type, as a pointer is compatible with (some) integer types:
pthread_t pid;
pthread_create(&pid, NULL, (void *(*)(void *))foo, (void *)argument));
However, you'd better wrap your function into another, pthread-compatible one, then return a pointer to its return value (must be free()'d after use):
void *foo_wrapper(void *arg)
{
    int a = *(int *)arg;
    bool retval = foo(a);
    bool *ret = malloc(sizeof(bool));
    *ret = retval;
    return ret;
}
then use:
pthread_t pid;
pthread_create(&pid, NULL, foo_wrapper, &a);
With this method, in the future you'll be able to call a function with arbitrary return or argument types.

                        
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