class A {public: A() { init(); } virtual void init() { printf("A::init\n"); }};class B : public A {public: B() { init(); } virtual void init() { print... Read More
class A {public: A() { printf("A \n"); } ~A() { printf(" ~A \n"); }// 这里不管写不写virtual,删除B对象的时候,都会被执行。因为这个例子是B*指针指向B对象,不是A*指针指向B对象。};class B : public A{... Read More
CREATE TABLE `test` ( `col1` VARCHAR( 10 ) CHARACTER SET utf8 COLLATE utf8_general_ci NOT NULL , `col2` VARCHAR( 10 ) CHARACTER SET utf8 COLLATE utf8_general_ci NULL) ENGINE = MYISAM ;错误(不可以插入null值):INSERT INTO `test` VALUES (null,1);正确(插入''没问题):INSERT INTO `test` VALUES ('',1);INSER Read More