stuff

Examples/ipc/ipcfs2.c

@@ -0,0 +1,59 @@
+/*
+ * ipcsfs2 - Using the file system for inter-process communication
+ *           Fixes the file position pointer problem in ipcfs1.c
+ *           by using lseek to reset the pointer to the beginning
+ *           Shows the frustration with using the file system for
+ *           IPC by needing to move the file position pointer around
+ */
+
+#include <fcntl.h>     // needed for open system call
+#include <stdio.h>     // needed for printf
+#include <stdlib.h>    // needed for exit
+#include <string.h>    // nneded for strlen
+#include <sys/types.h> // needed for pid_t
+#include <sys/wait.h>  // needed for wait system call
+#include <unistd.h>    // needed for fork, read, write, close system calls
+
+int main()
+{
+    // Open a file for reading and writing
+    // Create it if it doesn't exist
+    int myfile = open("MYFILE", O_RDWR | O_CREAT | O_TRUNC, S_IRUSR | S_IWUSR);
+
+    pid_t pid = fork(); // fork into 2 processes
+
+    if (pid < 0) // error
+    {
+        printf("ERROR: COULD NOT FORK\n");
+        exit(EXIT_FAILURE);
+    }
+    else if (pid == 0) // child
+    {
+        /* Write to parent */
+        char *data = "HELLO";
+        write(myfile, data, strlen(data));
+        printf("Child wrote %s\n", data);
+
+        /* Close file */
+        close(myfile);
+
+        return 0; // Return success
+    }
+    else // parent
+    {
+        /* Wait for child */
+        wait(0);
+
+        /* Reset file position pointer */
+        lseek(myfile, 0, SEEK_SET);
+
+        /* Read data */
+        char data[32];
+        read(myfile, data, sizeof(data));
+        printf("Parent received %s from child\n", data);
+
+        /* Close file */
+        close(myfile);
+    }
+    return 0; // Return success
+}