C ++ efficient programming: Reading Note 1

Mentioned in the last chapter of this bookAlgorithmHere are a few examples of the traps, and write down two.

1. Coverage of cyclic count

If you add 1 to a byte with a value of 255, the byte will change to 0.

UnsignedCharI;
For(I=0;I<256;I++){
Cout<"Test"<(Int)I<Endl;
}

In this case, an infinite loop occurs, because after 255, the value is 0 again.

2. Mixed Array and inheritance

# Include <iostream. h>

ClassAveragejoe
{
Public:
LongID;
};

ClassJetset:PublicAveragejoe
{
Public:
LongVIP;
};

VoidSetid(Averagejoe*Person,LongIndex,LongNumber){
Person[Index].ID=Number;
}

Void Main ( Void ) {
Jetsetvips [ 40 ];
For ( Int I = 0 ; I < 40 ; I ++) {
VIPs [ I ]. VIP = 1 ;
}
Setid ( VIPs , 1 , 0 );
If ( 1 = VIPs [ 0 ]. VIP ) {
Cout < "VIP !!! " < Endl ;
} Else {
Cout < "Not VIP ." < Endl ;
}
// Test
Cout < "Test: \ n" < "VIPS [1]. ID :" < VIPs [ 1 ]. ID < Endl ;
Cout < "VIPS [0]. VIP :" < VIPs [ 0 ]. VIP < Endl ;
}

 

The size of a class averagejoe is 4 bytes, while that of Jetset is 8 bytes. When the setid function is called, the pointer is operated according to the size of averagejoe, and 4 bytes are moved each time.
Solution: Define the setid function as a member function of the base class.