如何解决使用线程时内存分配问题
我正在尝试与使用数据分配的结构一起使用。尽管在每个函数中都获得了正确的输出,但是当这些函数通过线程运行时,我仍然遇到了溢出错误。我当前拥有的代码是:
#include <iostream> // cout,endl
#include <thread> // thread
using namespace std;
// a structure to hold parameters to pass to a thread
struct StatData
{
// the number of numbers
int n;
// the array of numbers
double *numbers;
};
void average(StatData *data,double *avg) {
int id;
int size = data->n;
double sum = 0.0;
for(int i = 0; i < size; i++){
sum += data->numbers[i];
}
*avg = sum / size;
}
void minimum(StatData *data,double *min) {
int id;
int size = data->n;
*min = data->numbers[0];
for(int i = 0; i < size; i++){
if (*min > data->numbers[i]){
*min = data->numbers[i];
}
}
}
void maximum(StatData *data,double *max) {
int id;
int size = data->n;
*max = data->numbers[0];
for(int i = 0; i < size; i++){
if (*max < data->numbers[i]){
*max = data->numbers[i];
}
}
}
int main(int argc,char** argv) {
// checking if arguments were passed
if (argc <= 1) {
cout << "No numbers were passed." << endl;
cout << "At least one number needs to be entered." << endl;
return 1;
}
// declaring worker threads
thread avg_t,min_t,max_t;
// variables for values
double avg_v;
double min_v;
double max_v;
// initalizing data structure to hold numbers
StatData data;
data.n = argc - 1; // the amount of numbers passed
data.numbers = new double[data.n]; // allocating space for nums
// Filling in the array with numbers using atof
for (int i = 0; i < data.n; i++) {
data.numbers[i] = atof(argv[i+1]); // converting string to double
}
// creating average thread
avg_t = thread(average,&data,&avg_v);
// creating minimum thread
min_t = thread(minimum,&min_v);
// creating maximum thread
max_t = thread(maximum,&max_v);
// wating for threads to finish
avg_t.join();
min_t.join();
max_t.join();
printf ("The average value is %d\n",&avg_v);
printf ("The minimum value is %d\n",&min_v);
printf ("The maximum value is %d\n",&max_v);
// freeing up dynamically allocated space
delete[] data.numbers;
}
当我以47、58和6的值运行./test时,我得到以下打印声明: 平均值是-502425280 最小值是-502425288 最大值为-502425296
我不确定我要去哪里出错导致代码执行此操作。
解决方法
您正在打印值的地址(&avg_v
是指向avg_v
的指针,当打印为%d
时,它将打印指针本身的一部分值)。
要自己打印double
值,只需执行
printf ("The average value is %lf\n",avg_v);
printf ("The minimum value is %lf\n",min_v);
printf ("The maximum value is %lf\n",max_v);
请注意,%d
用于打印整数,对于浮点值,请使用%f
或%lf
(二者等效)。
&
中需要 scanf
,因为scanf
采用变量的地址。 printf
采用实际值,因此无需将地址传递给它(除非您当然要打印地址)。
经过整理,可以说该程序可以通过使用更多C ++标准库功能来简化。仅举几例:std::vector
,std::accumulate
,std::min_element
,std::max_element
,std::async
(将为您创建线程并返回未来)和lambda:
#include <iostream>
#include <thread>
#include <vector>
#include <numeric>
#include <algorithm>
#include <future>
int main(int argc,char** argv) {
if (argc <= 1) {
std::cout << "No numbers were passed.\n"
"At least one number needs to be entered.\n";
return 1;
}
std::vector<double> data;
for (int i = 1; i < argc; i++) {
data.push_back(atof(argv[i]));
}
auto avg_f = std::async([&] {
return accumulate(data.begin(),data.end(),0.0) / data.size();
});
auto min_f = std::async([&] {
return *min_element(data.begin(),data.end());
});
auto max_f = std::async([&] {
return *max_element(data.begin(),data.end());
});
// the 3 values are now being computed in parallel ...
double avg_v = avg_f.get(); // get the values from futures (waits as necessary)
double min_v = min_f.get();
double max_v = max_f.get();
std::cout << "The average value is " << avg_v << "\n";
std::cout << "The minimum value is " << min_v << "\n";
std::cout << "The maximum value is " << max_v << "\n";
}
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