map iterator

[thomas]

a question about map iterator

---code---
#include<map>
#include<iterat or>
using namespace std;

int main(){
map<string,int mp;
mp.insert(pair< string,int>("he llo",1));
for(map<string, int>::iterator it(mp.begin()); it<mp.end(); it+
+) ///----L---
cout<<it->first<<endl;
}
----code ----

it cannot compile; if I change the "it<mp.end( )" to "it!=mp.end ()"
in line L , it works.

for int vectors, I can use "it<vi.end( )" to make boundary check, but
for map it doesn't works.

any explaination or suggestions?

[Andrew Koenig]

Re: map iterator

"thomas" <FreshThomas@gm ail.comwrote in message
news:5a901f5a-4d58-4e95-9cff-a3d316ecfa81@y3 8g2000hsy.googl egroups.com...

for int vectors, I can use "it<vi.end( )" to make boundary check, but
for map it doesn't works.

any explaination or suggestions?

Vector iterators are random-access iterators. Map iterators aren't. If
this doesn't answer your question completely, please study the definition of
random-access iterators carefully.

[Daniel T.]

Re: map iterator

"Andrew Koenig" <ark@acm.orgwro te:

"thomas" <FreshThomas@gm ail.comwrote:
>

for int vectors, I can use "it<vi.end( )" to make boundary check, but
for map it doesn't works.

any explaination or suggestions?

>
Vector iterators are random-access iterators. Map iterators aren't. If
this doesn't answer your question completely, please study the definition of
random-access iterators carefully.

It might also help to know that map's iterator is a bidirectional
iterator. Studying the difference between random-access iterators and
bidirectional iterators might be helpful.

[Jim Langston]

Re: map iterator

"thomas" <FreshThomas@gm ail.comwrote in message
news:5a901f5a-4d58-4e95-9cff-a3d316ecfa81@y3 8g2000hsy.googl egroups.com...

>a question about map iterator
>
---code---
#include<map>
#include<iterat or>
using namespace std;
>
int main(){
map<string,int mp;
mp.insert(pair< string,int>("he llo",1));
for(map<string, int>::iterator it(mp.begin()); it<mp.end(); it+
+) ///----L---
cout<<it->first<<endl;
}
----code ----
>
it cannot compile; if I change the "it<mp.end( )" to "it!=mp.end ()"
in line L , it works.
>
for int vectors, I can use "it<vi.end( )" to make boundary check, but
for map it doesn't works.
>
any explaination or suggestions?

You've already gotten the explanation. The suggestion is instead of using <
use !=

for(map<string, int>::iterator it(mp.begin()); it != mp.end(); ++it) {
cout<<it->first<<endl;
}