struct tree{

struct tree *left;

struct tree *right;

};

typedef struct tree newtree;

int main(int argc, const char * argv[]) {

// insert code here...

printf("Hello, World!\n");

newtree *root = (newtree *)malloc(sizeof(newtree));

newtree temp;

printf("%d %d\n", root->left == NULL, temp.left == NULL);  //0 1 || 1 1

printf("%ld\n", sizeof(newtree));  //每个指针8个字节

return 0;

}

1. 初步来看结构体，malloc的东西不初始化。声明的局部变量temp是初始化的。