Iteration into std::vector<string> - c++

Question

I have a vector of string parameters...
|name1|value1|name2|value2|...
I wanna iterate and cache the name into a string and add it into a vector of names and make the same thing with the value. They are in a std::vector<string>.
I do it:
std::vector<string> names;
std::vector<string> values;
std::vector<string>::iterator pit = p.begin();
while(pit != p.end()){
string name = *pit;
pit++;
string value = *pit;
pit++;
names.push_back(name);
values.push_back(value);
}
But it returns an access violation in vector. It is accessing a bad location returning a <BadPtr>.
How to do this iteration?
Does it have a way of do it using for each?

Answer 1

Check this out:
std::vector<string> names;
std::vector<string> values;
std::vector<string>::iterator pit = p.begin();
while(pit != p.end()){
string name = *pit;
pit++;
if(pit == p.end())
break;
string value = *pit;
pit++;
names.push_back(name);
values.push_back(name);
}
As i said in my comment that problem could be, you didn't put any checking after incrementing pit second time.

Answer 2

Here is a demonstrative program that shows how it can be done using standard algorithm std::partition_copy
#include <iostream>
#include <vector>
#include <string>
#include <iterator>
#include <algorithm>
int main()
{
std::vector<std::string> p = { "name1", "value1", "name2", "value2" };
std::vector<std::string> names;
std::vector<std::string> values;
names.reserve( ( p.size() + 1 ) / 2 );
values.reserve( p.size() / 2 );
unsigned int i = 0;
std::partition_copy( p.begin(), p.end(),
std::back_inserter( names ),
std::back_inserter( values ),
[&]( const std::string & ) { return i ^= 1; } );
for ( const auto &s : p ) std::cout << s << ' ';
std::cout << std::endl;
for ( const auto &s : names ) std::cout << s << ' ';
std::cout << std::endl;
for ( const auto &s : values ) std::cout << s << ' ';
std::cout << std::endl;
return 0;
}
The program output is
name1 value1 name2 value2
name1 name2
value1 value2
The same can be done using the range based for statement
#include <iostream>
#include <vector>
#include <string>
int main()
{
std::vector<std::string> p = { "name1", "value1", "name2", "value2" };
std::vector<std::string> names;
std::vector<std::string> values;
names.reserve( ( p.size() + 1 ) / 2 );
values.reserve( p.size() / 2 );
unsigned int i = 0;
for ( const std::string &s : p )
{
if ( i ^= 1 ) names.push_back( s );
else values.push_back( s );
}
for ( const auto &s : p ) std::cout << s << ' ';
std::cout << std::endl;
for ( const auto &s : names ) std::cout << s << ' ';
std::cout << std::endl;
for ( const auto &s : values ) std::cout << s << ' ';
std::cout << std::endl;
return 0;
}
Thus your loop can look more simpler like
unsigned int i = 0;
for ( const std::string &s : p )
{
if ( i ^= 1 ) names.push_back( s );
else values.push_back( s );
}
As you see the body of the loop consists only from two statements instead of six or eight statements if to use your approach.