[015] downward type conversion and upward type conversion

1. Definition

Downward type conversion: Convert from parent class to subclass

Upward type conversion: Convert from subclass to parent class

2. Differences and risks

1) In general, the upward type conversion is safe, for example:

Base base;

Device dev;

Base = dev; convert to data

2) downward type conversion is dangerous because child classes may have other non-existent personalities of the parent class (adding member variables and functions ). For example:

Dev = base; downstream Data Conversion

The Slice problem is more likely to occur. To avoid this problem, we can use dynamic_cast to continue the downward type conversion.

Device * Dev = dynamic_cast <devece *> base; downstream Data Conversion

However, a failure may occur, so downward type conversion is not recommended.

[015] downward type conversion and upward type conversion