Google sparse_hash_map insertion doen't work when reading chars from the input file

Question

So, I'm noob in C++ and I'm trying to use sparse_hash_map but I can't figure out why insertion into the map does not work when reading the lines from the file, but it works when I hardcode strings.

#include <fstream>
#include <string>
#include <iostream>
#include <sstream>
#include <sparsehash/sparse_hash_map>

using google::sparse_hash_map;
using std::cout;
using std::endl;
using std::tr1::hash;


struct eqstr {
    bool operator()(const char* s1, const char* s2) const {
        return (s1 == s2) || (s1 && s2 && strcmp(s1, s2) == 0);
    }
};

int main() {
    sparse_hash_map<const char*, int, hash<const char*>, eqstr> map;

    std::string str1 = "test data 1";
    const char * c1 = str1.c_str();
    std::string str2 = "test data 2";
    const char * c2 = str2.c_str();
    std::string str3 = "test data 3";
    const char * c3 = str3.c_str();

    map[c1] = 1;
    map[c2] = 1;
    map[c3] = 1;

    cout << "Total: " << map.size() << endl; // 3

    std::string tmpStr;
    std::ifstream file;
    file.open("/usr/src/test.data");
    while (getline(file, tmpStr)) {
        const char * c = tmpStr.c_str();
        cout << c << endl; // prints row
        map[c] = 1;
    }

    cout << "Total: " << map.size() << endl; // prints 4, but obviously it should print 9. 
}

It always inserts only the first row from the file, but works when using hardcoded strings.

/usr/src/test.data

row 1
row 2
row 3
row 4
row 5
row 6

My code was compiled with g++ (Debian 4.9.2-10) 4.9.2

__cplusplus 199711L

I installed the library using the notes inside readme file (./configure, make, make install)