marcinwol · July 3, 2015 00:38 · Jul 3, 2015
diff --git a/return_value.cpp b/return_value.cpp
@@ -0,0 +1,64 @@
+/**
+ * Example of returning a value from threads
+ */
+
+#include <iostream>
+#include <vector>
+#include <mutex>
+#include <thread>
+
+using namespace std;
+
+// global mutex
+mutex process_mutex;
+
+
+struct S {
+    size_t x;
+};
+
+
+void calculate(S s, int& result) {
+    int out = s.x * 2;
+
+    {
+        // gard access to the sheared resource, i.e. cout
+        lock_guard<mutex> lock(process_mutex);
+        cout << "threadid=" << this_thread::get_id()
+             <<": x=" << s.x << " out=" << out << endl;
+    }
+
+    result = out;
+
+}
+
+int main() {
+
+
+    size_t no_of_threads = 5;
+
+    // this will store the values calculated by thread.
+    vector<int> results(no_of_threads, 0);
+
+    // vector of threads
+    vector<thread> threads;
+
+    // create threads
+    for(size_t i = 0; i < no_of_threads; ++i) {
+        threads.emplace_back(&calculate, S{i}, ref(results.at(i)));
+    }
+
+    // wait for their completion and display results.
+    for(size_t i = 0; i < no_of_threads; ++i) {
+        threads.at(i).join();
+    }
+
+    cout << endl << endl;
+
+    // display results.
+    for(size_t i = 0; i < no_of_threads; ++i) {
+        cout << "x=" << i << " out=" << results.at(i) << endl;
+    }
+
+    return 0;
+}