Open database file and read user input.

cstack · cstack · commit ad5fcd4bf99e · 2017-08-31T10:58:19.000-07:00
diff --git a/.gitignore b/.gitignore
@@ -0,0 +1,2 @@
+db
+*.db
diff --git a/Makefile b/Makefile
@@ -0,0 +1,11 @@
+db: db.c
+	gcc db.c -o db
+
+run: db
+	./db mydb.db
+
+clean:
+	rm -f db *.db
+
+format: *.c
+	clang-format -style=Google -i *.c
diff --git a/db.c b/db.c
@@ -0,0 +1,86 @@
+#include <fcntl.h>
+#include <stdbool.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+
+struct Connection_t {
+  int file_descriptor;
+};
+typedef struct Connection_t Connection;
+
+Connection* open_connection(char* filename) {
+  int fd = open(filename,
+                O_RDWR |      // Read/Write mode
+                    O_CREAT,  // Create file if it does not exist
+                S_IWUSR |     // Create file with user write permission
+                    S_IRUSR   // Create file with user read permission
+                );
+
+  if (fd == -1) {
+    printf("Unable to open file '%s'\n", filename);
+    exit(EXIT_FAILURE);
+  }
+
+  Connection* connection = malloc(sizeof(Connection));
+  connection->file_descriptor = fd;
+
+  return connection;
+}
+
+char* get_db_filename(int argc, char* argv[]) {
+  if (argc < 2) {
+    printf("Must supply a filename for the database.\n");
+    exit(EXIT_FAILURE);
+  }
+  return argv[1];
+}
+
+struct InputBuffer_t {
+  char* buffer;
+  size_t buffer_length;
+  ssize_t input_length;
+};
+typedef struct InputBuffer_t InputBuffer;
+
+InputBuffer* new_input_buffer() {
+  InputBuffer* input_buffer = malloc(sizeof(InputBuffer));
+  input_buffer->buffer = NULL;
+  input_buffer->buffer_length = 0;
+  input_buffer->input_length = 0;
+
+  return input_buffer;
+}
+
+void print_prompt() { printf("db > "); }
+
+void read_input(InputBuffer* input_buffer) {
+  ssize_t bytes_read =
+      getline(&(input_buffer->buffer), &(input_buffer->buffer_length), stdin);
+
+  if (bytes_read <= 0) {
+    printf("Error reading input\n");
+    exit(EXIT_FAILURE);
+  }
+
+  // Ignore trailing newline
+  input_buffer->input_length = bytes_read - 1;
+  input_buffer->buffer[bytes_read - 1] = 0;
+}
+
+int main(int argc, char* argv[]) {
+  char* db_filename = get_db_filename(argc, argv);
+  Connection* connection = open_connection(db_filename);
+
+  InputBuffer* input_buffer = new_input_buffer();
+  while (true) {
+    print_prompt();
+    read_input(input_buffer);
+
+    if (strcmp(input_buffer->buffer, ".exit") == 0) {
+      exit(EXIT_SUCCESS);
+    } else {
+      printf("Unrecognized command '%s'.\n", input_buffer->buffer);
+    }
+  }
+}
