[C++]How to use erase of std map correctly

keywords: [C++]How to use erase of std map correctly

Origin Text: http://www.cnblogs.com/graphics/archive/2010/07/05/1771110.html

#include <iostream>
#include <map>
#include <string>
using namespace std ;

int main(void) 
{ 
    map<int, string> m ;
    m.insert(pair<int, string>(1, "abc")) ;
    m.insert(pair<int, string>(2, "def")) ;
    m.insert(pair<int, string>(3, "def")) ;
    m.insert(pair<int, string>(4, "ghi")) ;


    map<int, string>::iterator itor ;


    // Print m
    map<int, string>::const_iterator citor ;
    for (citor = m.begin(); citor != m.end(); ++citor)
    {
        cout << citor->first << ":" << citor->second << endl ;
    }

    return 0 ; 
} 

for (itor = m.begin(); itor != m.end(); ++itor)
{
    if (itor->second == "def")
    {
        //because map is associative container，iterator would be invalid when invoke erase
        m.erase(itor);
    }
}

for (itor = m.begin(); itor != m.end(); ++itor)
{
    if (itor->second != "def")
    {
        //++itor would be invoked twice, so it's possible to make iterator invalid.
        m.erase(itor++);
    }
}

for (itor = m.begin(); itor != m.end();)
{
    if (itor->second == "def")
    {
        m.erase(itor++) ;
    }
    else
    {
        ++itor;
    }
}

//erase would return a valid iterator when element deleted.
//notice that not all STL version would return value, erase of SGI STL would not return value, VC STL would be.
for (itor = m.begin(); itor != m.end();)
{
    if (itor->second == "def")
    {
        //erase would return the next element of current deleted element.
        itor = m.erase(itor);
    }
    else
    {
        ++itor;
    }
}

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