Cannot push C style strings into std::vector - c++

Question

I'm trying to push some const char* into a vector, but the vector remains unpopulated after performing the operations I would presume to fill it.
Here's my attempt, where dict is my command-line argument.
test.cc
#include <iostream>
#include <string>
#include <vector>
#include <fstream>
using namespace std;
int main(int argc, char **argv)
{
ifstream dict;
size_t dict_size;
dict.open(argv[1]); // Dictionary
vector<const char*> dictionary;
string line;
getline(dict, line);
while(!dict.fail()) {
dictionary.push_back(line.c_str());
getline(dict, line);
}
dict_size = dictionary.size();
for(int i = 0; i < dict_size; i++)
cout << "dictionary[" << i << "] is " << dictionary[i] << endl;
}
dict
Hello
World
Foo
Bar
After compiling this, I get the following output:
dictionary[0] is
dictionary[1] is
dictionary[2] is
dictionary[3] is
However, if I change the dictionary's type to vector and push back line instead of line.c_str(), I get the expected output:
dictionary[0] is Hello
dictionary[1] is World
dictionary[2] is Foo
dictionary[3] is Bar
I'm not terribly familiar with C style strings, so maybe it has something to do with null termination?

Answer 1

You are storing dangling pointers.
std::string::c_str() isn't a pointer to some permanent copy of data — just think, that would be leaked!
Store the std::strings instead.

Answer 2

Your code invokes undefined behavior, because after you do
dictionary.push_back(line.c_str());
On the next line that pointer may get deleted:
getline(dict, line); // line now is a different string

Answer 3

You are pushing into the dictionary pointers that point to the same address and at the last iteration it fills the memory area with an empty string. If you don't care about memory leakage you can try like this:
#include <iostream>
#include <string>
#include <vector>
#include <fstream>
using namespace std;
int main(int argc, char **argv)
{
ifstream dict;
size_t dict_size;
dict.open(argv[1]); // Dictionary
vector<char *> dictionary;
while(!dict.fail()) {
string * line = new string();
getline(dict, *line);
if(line->length()>0)
{
dictionary.push_back((char *)line->c_str());
}
}
dict_size = dictionary.size();
for(int i = 0; i < dict_size; i++)
cout << "dictionary[" << i << "] is " << dictionary[i] << endl;
}