Sub: Update test_type

Body:

==== End ====

.gitignore

@@ -14,6 +14,8 @@ _book
 *.so
 *.swp
 *.swo
+*.bin
+*.dat
 
 # Byte-compiled / optimized / DLL files
 **/__pycache__/

snippet/cpp/test_type.c

@@ -1,6 +1,41 @@
 #include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <sys/time.h>
+
+typedef struct {
+    long long id;
+    char name[40];
+    char title[100];
+    long long create_time;
+} __attribute__((packed)) Person4;
+
+/*
+ * 编译器默认对 struct 的内存布局做对齐优化
+ * 添加 __attribute__((packed)) 取消对齐优化
+ */
+typedef struct {
+    long long id;
+    char name[40];
+    char title[100];
+    long long create_time;
+} Person;
+
+long long current_timestamp() {
+    long long tmp = 0;
+    struct timeval tval;
+    gettimeofday(&tval, NULL);
+    tmp = tval.tv_sec;
+    tmp = tmp * 1000;
+    tmp = tmp + tval.tv_usec / 1000;
+    return tmp;
+}
 
 int main(int argc, char **argv) {
+    Person *p = NULL;
+    char *filename = "tmp.dat";
+    FILE *fp = fopen(filename, "w");
+
     // there is no type of byte in c
     // printf("Size of byte: %d bytes\n", sizeof(byte));
     printf("Size of char: %lu bytes\n", sizeof(char));
@@ -25,5 +60,30 @@ int main(int argc, char **argv) {
      * Size of double: 8 bytes
      * Size of long double: 16 bytes
      */
+
+    long size_p = sizeof(Person);
+    long size_p4 = sizeof(Person4);
+    /* 取消优化后 Person4 的大小为 156 bytes，优化的 Person 大小为 160 bytes */
+    printf("Size of Person: %ld, Size of Person4: %ld\n", size_p, size_p4);
+    p = (Person *)malloc(size_p);
+    memset(p, 0, size_p);
+
+    p->id = 1L;
+    strcpy(p->name, "小明");
+    strcpy(p->title, "宇宙无敌暴龙战神");
+    p->create_time = current_timestamp();
+    char *buf = (char *)p;
+    fwrite(buf, sizeof(char), size_p, fp);
+    fclose(fp);
+
+    fp = fopen(filename, "r");
+    char *buf_read = (char *)malloc(size_p);
+    fread(buf_read, sizeof(char), size_p, fp);
+    Person *q = (Person *)buf_read;
+    printf("Person q, size: %ld bytes, id: %lld, name: %s, title: %s, create_time: %lld\n", 
+           size_p, q->id, q->name, q->title, q->create_time);
+    fclose(fp);
+
+    free(p);
     return 0;
 }