1. C++ Concerns: Timing Code, Random Numbers, Memory

2. Timing Method 1 : Stop watch
Measure real "wall" time from start to end
Other processes may have very direct impact

3. Timing Method 2 : Use OS tools to track process time
*nix: "time myprogram.exe"
Windows: use PowerShell and: "Measure-Command { myProgram.exe | Out-default }" Wall time only!

4. Instrumented Timing Method 3 : instrument code
Add code to record elapsed processor time between points in code
Targeted timing

5. <ctime> <ctime> library includes
clock() : units of time since program launch
c_type : type of data returned by clock()
typedef of long on win32 g++
CLOCKS_PER_SECOND : defined value
Integral type – careful with division
1000 on w32 g++

6. Timing Issues On Windows, clock() measures wall time elapsed
On linux processor time elapsed
Hard to measure short events
Wrap in a loop and average

7. High Resolution Timing
C++11 <chrono> library:
May support < 1 ms timers
Not on Windows (or in VM if host OS is windows)

8. Random Numbers

9. Random Test Data w/CStdLib
Need cstdlib, possibly ctime
srand(int) to seed
rand() to get random integer

10. Random Test Data w/CStdLib
Seed with:
Constant for same sequence each time
Time for random sequence
Seed only ONCE per program

11. Random Test Data w/CStdLib
Want a number between 0 & 1 millionish

12. Random Test Data w/CStdLib
Want a number between 0 & 1 millionish
Bad recipes:
rand() only up to 32,000
rand() * 30 can only generate multiples of 30
number = 0 repeat 30 times: number += rand() normal distribution

13. Random Test Data w/CStdLib
Better recipe for 0-999,999 :

14. Random with C++11 Random library:
Random Engine: Object that can generate sequences

15. Random with C++11
Distribution: object that maps generated values onto desired range:
Distribution object operates on generator to produce value:

16. Stack vs Heap

17. Stack = limited space
Values allocated on the stack have limited lifespan
VERY limited space available
Large arrays will crash program at start

18. Heap = Heap allocations (using new) live until deleted
Large amounts of space available
Where you need to put any large arrays