C++ reading random lines of txt?

I am running C++ code where I need to import data from txt file. The text file contains 10,000 lines. Each line contains n columns of binary data.

The code has to loop 100,000 times, each time it has to randomly select a line out of the txt file and assign the binary values in the columns to some variables.

What is the most efficient way to write this code? should I load the file first into the memory or should I randomly open a random line number?

How can I implement this in C++?

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To randomly access a line in a text file, all lines need to have the same byte-length. If you don't have that, you need to loop until you get at the correct line. Since this will be pretty slow for so much access, better just load it into a std::vector of std::string s, each entry being one line (this is easily done with std::getline ). Or since you want to assign values from the different columns, you can use a std::vector with your own struct like

struct MyValues{
  double d;
  int i;
  // whatever you have / need
};

std::vector<MyValues> vec;

Which might be better instead of parsing the line all the time.

With the std::vector , you get your random access and only have to loop once through the whole file.

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10K lines is a pretty small file. If you have, say, 100 chars per line, it will use the HUGE amount of 1MB of your RAM.

Load it to a vector and access it the way you want.

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maybe not THE most efficient, but you could try this:

int main() {
    //use ifstream to read
    ifstream in("yourfile.txt");

    //string to store the line
    string line = "";

    //random number generator
    srand(time(NULL));

    for(int i = 0; i < 100000; i++) {
        in.seekg(rand() % 10000);
        in>>line;
        //do what you want with the line here...
    }
}

Im too lazy right now, but you need to make sure that you check your ifstream for errors like end-of-file, index-out-of-bounds, etc...

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