Initial commit

Problem 3.20/main.c

@@ -0,0 +1,52 @@
+#include <stdlib.h>
+#include <stdio.h>
+#include <unistd.h>
+#include <string.h>
+#include <errno.h>
+#include <fcntl.h>
+#define SIZE 65536
+
+int main(int argc, char *argv[]) {
+    int pipefd[2];          // pipefd[0] represents input stream id, pipefd[1] represents output stream id.
+    char buffer[SIZE];      // The buffer of main process.
+    char childBuffer[SIZE]; // The buffer of sub-process.
+
+    // If the number of arguments is not correct.
+    if (argc != 3) {
+        perror("Main: main [target] [destination].\n");
+        return 1;
+    }
+
+    char *srcFile = argv[1]; // Source
+    char *dstFile = argv[2]; // Destination
+
+    // Building a pipe. If the returned integer is less than 0,
+    if (pipe(pipefd) < 0) {
+        printf("An error occured when createing the pipe: %s\n", strerror(errno));
+        return 1;
+    }
+    
+    pid_t pid = fork(); // Create a sub-process.
+
+    if (pid == 0) {         // pid == 0 represents it's a sub-process.
+        close(pipefd[1]);   // Close pipefd[1]
+        ssize_t file_size = read(pipefd[0], childBuffer, sizeof(childBuffer));  // Get the size of child
+        close(pipefd[0]);                                       // Close pipefd[0] since it is unable to use.
+        int dst_file_fd = open(dstFile, O_CREAT | O_WRONLY);    //  Read a file in writeonly mode. If the file does not exit, create a new one.
+        write(dst_file_fd, childBuffer, file_size);             // Write data from buffer into fd.
+        close(dst_file_fd);                                     // Close file
+    }
+    else if (pid > 0) { // pid > 0 represents it's a main process.
+        close(pipefd[0]);                                                   // Close pipefd[0]
+        int target_file_fd = open(srcFile, O_RDONLY);                       // Open a file in readonly mode.
+        ssize_t file_size = read(target_file_fd, buffer, sizeof(buffer));   // Get size of the file
+        write(pipefd[1], buffer, file_size);                                // Write data from buffer into pipefd[1]
+        close(pipefd[1]);                                                   // Close pipefd[1]
+        close(target_file_fd);                                              // Close file
+    }
+    else { // When error occur
+        printf("An error occured when forking child process. %s\n", strerror(errno));
+        return 1;
+    }
+    return 0;
+}