what is the difference between size() and length() function of c++ string if they give the same output?

Question

2.00/5 (2 votes)

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In the following code how can we differentiate between size() and length() of string ?

C++

#include<iostream.h>
#include<conio.h>
using namespace std;
int main()
{
   char a[5]="abc";
    
    cout<<sizeof(a);
    cout<<endl;
    
    string s;
    s=a;
    cout<<s.length();
    cout<<endl;
    cout<<s.size();
    cout<<endl;
    
    string b[3];
    cout<<"Size of string :"<<s.size()<<endl;
    b[0]="abcd";
    cout<<"Size of string :"<<s.length();
    getch();
    return 0;
}

Posted 5-Sep-12 6:30am

Ashutosh_g

Updated 5-Sep-12 6:32am

Wes Aday

v2

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Comments

[no name] 5-Sep-12 12:34pm

size_t size() const;Return length of string Returns a count of the number of characters in the string. string::length is an alias of string::size, returning both the exact same value. http://www.cplusplus.com/reference/string/string/size/

Philip Stuyck 5-Sep-12 13:02pm

counts as an answer if you ask me ;-)

Albert Holguin 5-Sep-12 13:36pm

I think that pretty much is the answer... think Wes must've been doubting something.

Sergey Alexandrovich Kryukov 5-Sep-12 14:09pm

I think this is the Wes's style. He post a great number of very good comments to the questions, and many would make good answers. I wish I could up-voted them.
--SA

[no name] 5-Sep-12 14:35pm

No need. Wes finds it hard to care about too much these days. Points are not important.

Sergey Alexandrovich Kryukov 5-Sep-12 18:50pm

Right, but the form of the answer is more visible and hence useful...
--SA

Albert Holguin 5-Sep-12 20:18pm

Wes is talking about himself in third person... It may be time for Wes to take a vacation. :)

[no name] 5-Sep-12 21:28pm

Yes... a vacation... Let's call it a "vacation"... Wes is going on a long vacation, soon.

Sergey Alexandrovich Kryukov 5-Sep-12 14:07pm

Yes, my 5.
--SA

Albert Holguin 5-Sep-12 13:36pm

+5? ...lol... I posted your answer along with a bit more info of how this probably came about.

2 solutions

Solution 2

Maybe not a strictly formal answer, but I've seen the convention that 'size' refers to the number of bytes, and 'length' refers to the number of elements. So for a char array, the size and length are the same, but for arrays of other data types the size would be greater.

Posted 5-Jan-15 10:33am

chris stolarik

Comments

enhzflep 6-Jan-15 0:32am

That may well be the case for other data-types, but don't forget - we're dealing with the std::string class here. This answer really doesn't add anything to the topic, in my opinion.

Realizing that std::wstring is the wide-char version of a std::string, we can use them with the same syntax, yet different input data. If you try to compare the size and length of a string with the size and length of a wstring, you get the exact same answer. In each case, the returned value is the number of characters in the string.

An example: (sorry for the lack of formatting)

---------------------------8<--------------------------
#include <iostream>

using namespace std;

int main()
{
wstring mWideString = L"This is a string";
string mCharString = "This is a string";

wcout << mWideString << endl;
cout << mCharString << endl;

cout << "Wide String:" << endl;
cout << "Size: " << mWideString.size() << endl;
cout << "Length: " << mWideString.length() << endl;
cout << endl;

cout << "Narrow String:" << endl;
cout << "Size: " << mCharString.size() << endl;
cout << "Length: " << mCharString.length() << endl;
cout << endl;
}
---------------------------8<--------------------------

Output:
=======
This is a string
This is a string
Wide String:
Size: 16
Length: 16

Narrow String:
Size: 16
Length: 16

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Albert Holguin · Accepted Answer · 2012-09-05T07:29:00

Solution 1

As Wes answered in the comments... it's just an alias...

See here[^]

There's probably some sort of historical reason why there's two methods that do the same exact thing, but it's really irrelevant at this point. I'd recommend you use only one version in your code since it'll make it more readable and easier to support in the long run (if they decide to eliminate one or the other in the future it'll be easier to fix).

Posted 5-Sep-12 7:29am

Albert Holguin

Comments

Sergey Alexandrovich Kryukov 5-Sep-12 14:07pm

5ed, but Wes does deserve 5, too.
--SA

Albert Holguin 5-Sep-12 14:28pm

Of course... He's eternally stuck on comments... :)

[no name] 5-Sep-12 14:19pm

Of course, 5

Albert Holguin 5-Sep-12 14:28pm

Thanks Wes.. Of course, you deserve the credit for this one. Post more answers and less comments... :p

Sergey Alexandrovich Kryukov 5-Sep-12 18:50pm

@Wes: I agree. I wish I could up-vote many of your comments; they are very good.
--SA

Philip Stuyck 5-Sep-12 15:42pm

+5