Nonamed pipes example

Author: optiklab

multithreading/12 - Nonamed_pipes.cpp

@@ -0,0 +1,132 @@
+#include <iostream>
+#include <stdio.h>
+#include <stdlib.h>
+#include <unistd.h>
+#include <sys/types.h>
+#include <sys/wait.h>
+
+using namespace std;
+
+struct CmdLine
+{
+    char* value;
+    char* arguments;
+    CmdLine* next;
+};
+
+// Compilation:
+// g++ "03 - Nonamed_pipes.cpp" -o nonamedpipes
+
+// Task:
+// Create a program which works just like the command below:
+// $> who | sort | uniq -c | sort -nk1
+
+void run(CmdLine* command)
+{
+    const int numPipes = 3;
+    int i = 0;
+
+    // Create all pipes.
+    int pipefds[2*numPipes];
+    for(i = 0; i < (numPipes); i++)
+    {
+        if(pipe(pipefds + i*2) < 0)
+        {
+            printf("Couldn't create pipe %d\n", i + 1);
+            exit(EXIT_FAILURE);
+        }
+    }
+    
+    int j = 0;
+    pid_t pid;
+    while(command)
+    {
+        pid = fork();
+        if(pid == 0)
+        {
+            //if not last command
+            if(command->next)
+            {
+                if(dup2(pipefds[j + 1], STDOUT_FILENO) < 0)
+                {
+                    perror("dup2");
+                    exit(EXIT_FAILURE);
+                }
+            }
+
+            //if not first command && j != 2*numPipes
+            if(j != 0 )
+            {
+                if(dup2(pipefds[j-2], STDIN_FILENO) < 0)
+                {
+                    perror(" dup2");///j-2 0 j+1 1
+                    exit(EXIT_FAILURE);
+                }
+            }
+
+
+            for(i = 0; i < 2*numPipes; i++)
+            {
+                close(pipefds[i]);
+            }
+            
+            // Command with or without arguments.
+            if (command->arguments == NULL)
+            {
+                if( execlp(command->value, command->value, NULL) < 0 )
+                {
+                    perror(command->value);
+                    exit(EXIT_FAILURE);
+                }
+            }
+            else
+            {
+                if( execlp(command->value, command->value, command->arguments, NULL) < 0 )
+                {
+                    perror(command->value);
+                    exit(EXIT_FAILURE);
+                }
+            }
+        }
+        else if(pid < 0)
+        {
+            perror("error");
+            exit(EXIT_FAILURE);
+        }
+
+        command = command->next;
+        j+=2;
+    }
+    
+    /* Parent closes the pipes and wait for children */
+    for(i = 0; i < 2 * numPipes; i++)
+    {
+        close(pipefds[i]);
+    }
+
+    int status;
+    for(i = 0; i < numPipes + 1; i++)
+    {
+        wait(&status);
+    }
+}
+
+int main(int argc, char** argv)
+{
+    printf("Result of operation is the same like if you type\n$>who | sort | uniq -c | sort -nk1\n");
+    
+    char sort[] = "sort";
+    char sortArg[] = "-nk1";
+    char uniq[] = "uniq";
+    char uniqArg[] = "-c";
+    char who[] = "who";
+    
+    CmdLine command4 = { sort, sortArg, NULL };
+    CmdLine command3 = { uniq, uniqArg, &command4 };
+    CmdLine command2 = { sort, NULL, &command3 };
+    CmdLine command1 = { who, NULL, &command2 };
+    
+    run(&command1);
+    
+    return 0;
+}