sizeof () string is reported as 28 ???? Why????

[dwaach]

Hi,

In the following program,

#include <iostream>
using namespace std;

class A
{
public:
string name;
char address[256];
};


int main()
{
A oa;
cout<<sizeof(oa.name)<<endl;
cout<<sizeof(oa.address)<<endl;
return 0;
}

Output is,
28
256

Why is string size as 28.

???

Thanks
Abhi

 

[Ian Collins]

Hi,

In the following program,

#include <iostream>
using namespace std;

class A
{
public:
string name;
char address[256];
};


int main()
{
A oa;
cout<<sizeof(oa.name)<<endl;
cout<<sizeof(oa.address)<<endl;
return 0;
}

Output is,
28
256

Why is string size as 28.

What did you expect?

You are outputting the size of a std::string object, not the contents of
name.

 

[Roland Pibinger]

int main()
{
A oa;
cout<<sizeof(oa.name)<<endl;

cout << oa.name.length() << endl; // or oa.name.size()

cout<<sizeof(oa.address)<<endl;
return 0;
}

sizeof(oa.name) is the size of the string object. Your library uses
some implementation optimizations which make the object that large.

 

[nevergone]

#include <iostream>
using namespace std;

class A
{
public:
string name;
char address[256];

};

int main()
{
A oa;
cout<<sizeof(oa.name)<<endl;
cout<<sizeof(oa.address)<<endl;
return 0;

}

Output is,
28
256

Why is string size as 28.

???

Thanks
Abhi

in g++, ubuntu
the output is:
4
256

 

[Roland Pibinger]

in g++, ubuntu
the output is:
4
256

Impelentation and performance characteristics of string are not
standardized. g++ probably uses a ref-counted string implementation
with 'copy-on-write' whereas Microsoft/Dinkumware uses SSO (small
string optimization) with an internal buffer resulting in cheap
creation and copying for 'short' strings but expensive copying for
'long' strings.

 

[outmatch]

dwaach 写é“:

Hi,

In the following program,

#include <iostream>
using namespace std;

class A
{
public:
string name;
char address[256];
};


int main()
{
A oa;
cout<<sizeof(oa.name)<<endl;
cout<<sizeof(oa.address)<<endl;
return 0;
}

Output is,
28
256

Why is string size as 28.

???

Thanks
Abhi

sizeof(std::string) depends on different implemention. It could be only
a pointer, or a struct.