pair STL query

onkar

#include<iostream>
using namespace std;
int main(void){
const pair<const char*,const char*arr[]={
pair<const char*,const char*>("1","1"),
pair<const char*,const char*>("12","12"),
pair<const char*,const char*>("123","123"),
pair<const char*,const char*>("1234","1234"),
pair<const char*,const char*>("12345","12345"),
};
cout<<sizeof(char)<<endl;
cout<<sizeof(arr[0])<<endl;
cout<<sizeof arr<<endl;
cout<<sizeof(arr)/sizeof(arr[0])<<endl;
return 0;
}
gives me :

1
8 <- ????? Why ????
40
5

Jul 8 '06 #1

Ian Collins

onkar wrote:

#include<iostream>
using namespace std;
int main(void){
const pair<const char*,const char*arr[]={
pair<const char*,const char*>("1","1"),
pair<const char*,const char*>("12","12"),
pair<const char*,const char*>("123","123"),
pair<const char*,const char*>("1234","1234"),
pair<const char*,const char*>("12345","12345"),
};
cout<<sizeof(char)<<endl;
cout<<sizeof(arr[0])<<endl;
cout<<sizeof arr<<endl;
cout<<sizeof(arr)/sizeof(arr[0])<<endl;
return 0;
}
gives me :

1
8 <- ????? Why ????

2*sizeof(char*) ?

--
Ian Collins.

Jul 8 '06 #2

Rolf Magnus

onkar wrote:

#include<iostream>
using namespace std;
int main(void){
const pair<const char*,const char*arr[]={
pair<const char*,const char*>("1","1"),
pair<const char*,const char*>("12","12"),
pair<const char*,const char*>("123","123"),
pair<const char*,const char*>("1234","1234"),
pair<const char*,const char*>("12345","12345"),

Have a look at std::make_pair.

};
cout<<sizeof(char)<<endl;
cout<<sizeof(arr[0])<<endl;
cout<<sizeof arr<<endl;
cout<<sizeof(arr)/sizeof(arr[0])<<endl;
return 0;
}
gives me :

1
8 <- ????? Why ????

Why not? What did you expect?

40
5

Jul 8 '06 #3

sonison.james

Hi,

sizeof of STL containers does not return the size of the contained
object - sizeof vector<charcontaing 100 chars is not 100. You need to
check your STL implementation of pair to see why it is returning 8.
Thanks and regards
Sonison James
onkar wrote:

#include<iostream>
using namespace std;
int main(void){
const pair<const char*,const char*arr[]={
pair<const char*,const char*>("1","1"),
pair<const char*,const char*>("12","12"),
pair<const char*,const char*>("123","123"),
pair<const char*,const char*>("1234","1234"),
pair<const char*,const char*>("12345","12345"),
};
cout<<sizeof(char)<<endl;
cout<<sizeof(arr[0])<<endl;
cout<<sizeof arr<<endl;
cout<<sizeof(arr)/sizeof(arr[0])<<endl;
return 0;
}
gives me :

1
8 <- ????? Why ????
40
5

Jul 10 '06 #4

Richard Herring

In message <11*********************@b28g2000cwb.googlegroups. com>,
so***********@gmail.com writes

[Please don't top-post. Rearranged]

>onkar wrote:

>#include<iostream>
using namespace std;
int main(void){
const pair<const char*,const char*arr[]={
pair<const char*,const char*>("1","1"),
pair<const char*,const char*>("12","12"),
pair<const char*,const char*>("123","123"),
pair<const char*,const char*>("1234","1234"),
pair<const char*,const char*>("12345","12345"),
};
cout<<sizeof(char)<<endl;
cout<<sizeof(arr[0])<<endl;
cout<<sizeof arr<<endl;
cout<<sizeof(arr)/sizeof(arr[0])<<endl;
return 0;
}
gives me :

1
8 <- ????? Why ????
40
5

sizeof of STL containers does not return the size of the contained
object - sizeof vector<charcontaing 100 chars is not 100.

std::pair isn't a "container" the way vector is. It's just a templated
2-element structure.

>You need to
check your STL implementation of pair to see why it is returning 8.

What would you expect the size of the following to be?

struct {
const char * first;
const char * second;
};
--
Richard Herring

Jul 10 '06 #5