After while loop exits, contents of the string are being deleted? - c++

Question

Hey everyone this is my first post so if I make any mistakes, such as not enough info etc, please let me know so I do not make them again.
So my issue is I need to take the contents of a file and then input them into a string, which I have working. However after the while loop ends if I try to use that string outside the while loop and manipulate the contents the string. The string is blank and there seems to be no contents. I determined this by using std::cout lines. I believe this to be a scope issue but I am not sure how to fix it. Below is the code pertaining to the question, any tips or help would be greatly appreciated!
std::string str;
std::ifstream file;
while(!file.eof()){
getline(file, str);
std::cout << str << "";
}
file.close();
std::cout << str << "";
std::map<std::string, int> map;
for(int i = 0; i < str.length(); ++i){
std::string sub = str.substr(i, k);
std::cout << sub << std::endl;
map.insert(make_pair(sub, 1));
}
std::cout << "" << std::endl;
Also, I am trying to chop the string up into size k which is a variable defined in a different part of the code, so I used the substr method in C++, and I believe this is working because when I put it in the while loop I can print out the contents of the file but the format is off and I think that is because of the nature of how the while loop runs, but I am not sure, please correct me if I am wrong or have any misconceptions.

Answer 1

Wouldn't it be easier to store the text file into a std::vector and then choose what sentence you'd want to manipulate?
Example:
int main()
{
std::string str;
std::ifstream file{ "file.txt" };
std::vector<std::string> vec;
// Store text file in vector
while (std::getline(file, str)) {
vec.emplace_back(str);
}
// Print out line 2:
std::cout << vec.at(1) << '\n';
// Reverse line 2 and print:
std::string line2 { vec.at(1) };
std::reverse(begin(line2), end(line2));
std::cout << line2 << '\n';
}

Answer 2

You are only storing one line at a time with getline(file, str);. My guess is that the last line of your file is blank, so the last value stored to str is blank.
You can concatenate instead of overwriting:
std::string temp;
std::string str;
std::ifstream file;
while(!file.eof()){
getline(file, temp);
std::cout << str << "";
str = str + temp;
}
Alternatively, add #include <fstream> and use:
std::ifstream inputStream("myfile.txt");
std::string str((std::istreambuf_iterator<char>(inputStream),
(std::istreambuf_iterator<char>()));