How to keep the buffer of std::cin after using std::cin.getline()

Question

I am trying to re-read the cin buffer after using cin.getline() 5 times, by calling cin.seekg(), but after calling cin.getline() again, instead of re-reading the data from the top, str becomes an empty string. Does cin.getline() flush the buffer? If so how do I stop that from happening?

#define PATH_MAX 512
using std::cin;

int main()
{
    char* str = new char[PATH_MAX + 1];

    for(int i = 0; i < 5; i++)
        cin.getline(str, PATH_MAX);

    cin.seekg(cin.beg);

    while(true)
        cin.getline(str, PATH_MAX);

    return 0;
}

Answer 1

I am trying to re-read the cin buffer after using cin.getline() 5 times

That's not possible with cin, terminal based input respectively.

What you can do is keeping track of the read input yourself, using a std::vector<std::string> keeping those lines read in 1st place. Here's a rough sketch:

#include <iostream>
#include <string>
#include <vector>    
using std::cin;
using std::string;

int main()
{
    std::vector<string> lines;
    string line;
    for(int i = 0; i < 5; i++) {
        std::getline(cin,line);
        lines.push_back(line);
    }

    auto linepos = lines.begin();
    while(linepos != lines.end()) {
        // cin.getline(str, PATH_MAX); instead do:
        // process *linepos
        ++linepos;
    }
}