add stucture pack

data/3.C语言高阶/3.位运算/7.对齐特性/pack01.md

+# 数的结构判断
+
+假设机器字是8 bytes，下面代码的占据的内存大小是多大？
+```c
+struct Test{
+    char *p;
+    char c;
+    int x;
+}
+```
+
+更多知识请参考：[失传的C结构体打包技艺](https://github.com/ludx/The-Lost-Art-of-C-Structure-Packing)
+
+## template
+
+```c
+struct Test{
+    char *p;
+    char c;
+    int x;
+};
+int main(int argc, char**){
+    print("%d", sizeof(struct Test))
+    return 0;
+}
+```
+
+## 答案
+
+```c
+8 bytes
+```
+
+## 选项
+
+### 选项1
+
+```c
+6 bytes
+```
+
+### 选项2
+
+```c
+9 bytes
+```
+
+### 选项3
+
+```c
+24 bytes
+```
\ No newline at end of file

data/3.C语言高阶/5.文件/2.文件的读写/file_hash.c

@@ -182,7 +182,14 @@ void sha256_read_hex(const struct sha256_buff *buff, char *hex) {
 }
 
 int main(int argc, char **argv) {
-  FILE *file = fopen(argv[1], "rb");
+
+  FILE *f1 = fopen("/tmp/c_hash_test.txt", "w+");
+  for (int i = 0; i < 1024; i++) {
+    fputs("Hello,World!", f1);
+  }
+  fclose(f1);
+
+  FILE *file = fopen("/tmp/c_hash_test.txt", "rb");
   if (!file) {
     printf("Cannot open file\n");
     return 0;