如何用线程修复代码中的C++错误C2672

Question

当我试图用线程编译程序时，C2672错误('voke'：找不到匹配的重载函数)正在发生。

我的代码：

#include <iostream>
#include <thread>
// the procedure for array 2 filling
void bar(int sum2)
{
for (int i = 100000; i < 200000; i++) {
sum2 = sum2 + (i + 1);
std::cout << sum2;
}
}
int main()
{
// the second counter initialization
int sum2 = 0;
// the constructor for the thread
std::cout << "staring thread2...n";
std::thread thread(bar);
// the thread detaching
thread.detach();
// the first counter initialization
int sum1 = 0;
// filling of the first array
for (int i = 0; i < 100000; i++) {
sum1 = sum1 + (i + 1);
// elements output
std::cout << sum1;
}
}

请告诉我，如何修复这个bug？

Answer 1

您需要将一个值传递给正在创建的线程

std::thread thread(bar, N);

其中N是整数值，正如您在void bar(int)函数中定义的那样。

#include <iostream>
#include <thread>
// the procedure for array 2 filling
void bar(int sum2)
{
for (int i = 100000; i < 200000; i++) {
sum2 = sum2 + (i + 1);
std::cout << sum2;
}
}
int main()
{
// the second counter initialization
int sum2 = 0;
// the constructor for the thread
std::cout << "staring thread2...n";
std::thread thread(bar, 100);
// the thread detaching
thread.detach();
// the first counter initialization
int sum1 = 0;
// filling of the first array
for (int i = 0; i < 100000; i++) {
sum1 = sum1 + (i + 1);
// elements output
std::cout << sum1;
}
return 0;
}

Answer 2

OP函数bar()的签名为：

void bar(int sum2)

因此，当函数传递给std::thread时，需要一个参数来初始化bar()函数参数int sum2。

当std::thread尝试在内部调用bar()时，它在没有任何参数的情况下这样做，但在没有参数的情况中不会重载bar()。因此，错误

C2672 error ('invoke': no matching overloaded function found)

它应该是std::thread thread(bar, sum2);或std::thread thread(bar, 0);或类似的东西而不是std::thread thread(bar);。

OP的固定示例(包括其他一些小调整)：

#include <iostream>
#include <sstream>
#include <thread>
// the procedure for array 2 filling
void bar(int sum2)
{
for (int i = 10/*0000*/; i < 20/*0000*/; i++) {
sum2 = sum2 + (i + 1);
std::cout << (std::ostringstream() << " 2: " << sum2).str();
}
}
int main()
{
// the second counter initialization
//int sum2 = 0; // UNUSED
// the constructor for the thread
std::cout << "staring thread2...n";
std::thread thread(bar, 0);
// the thread detaching
thread.detach();
// the first counter initialization
int sum1 = 0;
// filling of the first array
for (int i = 0; i < 10/*0000*/; i++) {
sum1 = sum1 + (i + 1);
// elements output
std::cout << (std::ostringstream() << " 1: " << sum1).str();
}
}

输出：

staring thread2...
1: 1 1: 3 1: 6 1: 10 1: 15 1: 21 1: 28 1: 36 1: 45 1: 55 2: 11 2: 23 2: 36 2: 50 2: 65 2: 81 2: 98 2: 116 2: 135 2: 155

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