Does adding additional headers make programs slower? - c++

Question

For instance would the following two programs have the save execution time?
#include <iostream>
int main()
{
int a,b;
std::cin >> a >> b;
std::cout << a+b;
return 0;
}
and
#include <ctime>
#include <cstdio>
#include <cstdlib>
#include <cstring>
#include <cassert>
#include <time.h>
#include <algorithm>
#include <iostream>
#include <vector>
int main()
{
int a,b;
std::cin >> a >> b;
std::cout << a+b;
return 0;
}
If so is it a good practice to always include a bunch of header files? How can one test how long it takes to execute a program? Using predefined input.

Answer 1

Does adding additional headers make programs slower?
No. Of course, someone will show up now with some corner case to refute this. But no, extra headers don't make C or C++ programs slower in general.
If so is it a good practice to always include a bunch of header files?
Don't include "a bunch." Include the ones you use. To include extra headers increases compilation time, and if the headers are from your own project, can result in recompiling many objects in your project whenever you touch any header.
How can one test how long it takes to execute a program?
With a stopwatch. Or time(). Or rdtsc. Or QueryPerformanceCounter(). Lots of ways.

Answer 2

For instance would the following two programs have the same execution time?
Yes. Including additional header files doesn't affect the execution time of the program.
Header files are processed at compile time. So they (usually) don't slow down your code.
There could be corner cases, that inclusion of particular headers might pickup a different implementation of some algorithm, that is inherently slower than a different one picked up without that header.
If so is it a good practice to always include a bunch of header files?
No. You should include the header file for every type you are using, no more no less.
How can one test how long it takes to execute a program? Using predefined input.
There are several possibilities to do that. You can run your program in a profiling tool, or simply measure time yourself (in a script or such).

Answer 3

Does adding additional headers make programs slower?
For instance, would the following two programs have the same execution time?
Adding additional headers won't affect the runtime of your program. It will affect the compile time however because the compiler now has to include these additional headers in your program.
If so is it a good practice to always include a bunch of header files?
It is best practice to only include the header files that you will be using in your project. Also, be careful not to include the C version of a header and the C++ version of a header, you may run into issues.
How can one test how long it takes to execute a program? Using predefined input.
I'd recommend checking out the ctime library: http://www.cplusplus.com/reference/ctime/
Remember that execution time is specific to your machine.

Answer 4

I think it will make the program slow because when ever you call a function like cout or cin compiler will find it in header files declared by programmer
More number of header files require more time to find the function definition
Also if including extra header files doesn't increase compilation time then ide(Integrated development environment) should have omit the header file including system
Hope that make sense