Comments on: 2.3 — Variable sizes and the sizeof operator

By: JD

JD — Mon, 30 Aug 2010 21:25:47 +0000

So, if I understand this correctly, the computer moves data around in 32-bit chunks (4 bytes), but in my C++ program I can assign variables to a single byte of memory. This seems contradictory to me.

I guess my question boils down to: Say I have a program that uses a large number of variables, so space matters. One byte will suffice for the data I need to carry so to save space I assign them as chars (1 byte). But, if the smallest “chunk” that the computer passes around is 4 bytes, does this actually save any space? Or would this effectively use the same amount of memory as if I made my variables ints (4 bytes, or one full word)?

This is a somewhat subtle question, so let me know if I’m not being clear.

PS – Thanks for a clear, organized, and well-written tutorial! I’ve really enjoyed it so far.

By: Gerald Parsons

Gerald Parsons — Sun, 18 Jul 2010 20:41:41 +0000

This tutorial is so easy. It makes learning
programing so easy. The problem comes once
you get out of C++ and try to understand
msdn help. These guys from Microsoft are from
outer space. Just try looking up some of the
things you learn here and see if you can get
anything that explains it in common english.
I could sure use a tutorial on how to use
Microsoft help, once you get to the help
you need. Some times they just go round and
round.

By: Anon

Anon — Wed, 03 Feb 2010 17:23:35 +0000

So does it really matter what variable type you use? Dont get me wrong i want to use the right one, but it seems a task to remember all of the maximum values etc.

is there a trick to it?

There’s an awful lot to choose from.

By: Mulky

Mulky — Wed, 06 Jan 2010 21:05:56 +0000

I bet you say that to all the ladies.

By: anonymous

anonymous — Sat, 01 Aug 2009 00:50:56 +0000

Greg, means you display the symbol of ‘\’, like ? or ! if ? or ! don’t work already. t shows , then the letter t. The reason is because ‘\’ isn’t a valid symbol for a string; the compiler seems to ignore it.

And also, a makes a beating sound. :) /

Sorry, can’t figure out why the backslash isn’t showing….

By: Alex

Alex — Sat, 02 May 2009 05:34:12 +0000

I present a better solution to this problem in lesson 0.7 -- a few common cpp problems

By: Alex

Alex — Sat, 02 May 2009 04:34:58 +0000

Why would you want to? :)

Stroustrup says here:

Sizeof cannot be overloaded because built-in operations, such as incrementing a pointer into an array implicitly depends on it. Consider:

X a[10];
X* p = &a[3];
X* q = &a[3];
p++; // p points to a[4]
// thus the integer value of p must be
// sizeof(X) larger than the integer value of q

Thus, sizeof(X) could not be given a new and different meaning by the programmer without violating basic language rules.

By: Emmet

Emmet — Sat, 18 Apr 2009 17:01:17 +0000

int y = 30, x = y * 1000;
	Sleep(x);

Why couldn't you say;

int y = 30000

Or better yet, just;

system("pause");
return 0;

By: Ranjan

Ranjan — Wed, 01 Apr 2009 16:02:22 +0000

what the resone behind it, why you can’t overload the size of operator ?

REgards,
Ranjan

By: James

James — Fri, 20 Mar 2009 07:08:57 +0000

Copy this code and use it on windows to keep the console screen up long enough for you to see the size of the data types... Also, I removed one \t from "wchar_t:\t\t" cuz a second tab caused that line to be out of alignment with the rest. y is the number of seconds you want the progam to wait before it ends.

#include 
#include 
int main()
{
	using namespace std;
	cout << "bool:\t\t" << sizeof(bool) << " bytes" << endl;
	cout << "char:\t\t" << sizeof(char) << " bytes" << endl;
	cout << "wchar_t:\t" << sizeof(wchar_t) << " bytes" << endl;
    cout << "short:\t\t" << sizeof(short) << " bytes" << endl;   
    cout << "int:\t\t" << sizeof(int) << " bytes" << endl;   
    cout << "long:\t\t" << sizeof(long) << " bytes" << endl;   
    cout << "float:\t\t" << sizeof(float) << " bytes" << endl;   
    cout << "double:\t\t" << sizeof(double) << " bytes" << endl;   
    cout << "long double:\t" << sizeof(long double) << " bytes" << endl;
	int y = 30, x = y * 1000; //assign y value of sleep time in seconds convert x to seconds 
	Sleep(x);
	return 0;
}

Oh, and alex, thanks for this tutorial. It's the most complete, comprehensive, explanatory, and easy to follow tut on c++ I've ever ran across. Thanks for the time u spent in creating it, making it public, and taking time to answer people's comments. You rock!