i/o vector of strings to text file

[Stauricus]

hello
i'm trying to write and read a vector of strings to/from a text file. it should count how many lines contain the word "here". but it does nothing.

void createTextFile(){
    std::vector<std::string> vetor(10000, "teeeeeeeeeeeeeeeeeeeeeeest");
    std::ofstream file("text.data");
    for (size_t n=0; n < vetor.size(); n+=5){
        vetor[n] = "here";
    }
    file.write(reinterpret_cast<char*>(&vetor[0]), vetor.size()*sizeof(vetor[0]));
}

void readTextFile(){
    std::vector<std::string> vetor;
    std::string line;
    std::ifstream file("text.data");
    int n = 0;
    while (file.good()){
        std::getline(file, line);
        if (line.find("here")!=std::string::npos){
                n++;
            std::cout << "found " << n << std::endl;
        }
    }
}

int main(){
    createTextFile();
    readTextFile();
    return 0;
}

what could i be doing wrong? thanks in advance.

[jlb]

Why are you using write() when using text mode? You probably should be using the insertion operator<< instead since you seem to expect each element of the vector to be on it's own line and you're not writing any new line characters to the stream. When you think you're writing "here" you're also writing a bunch of junk since you're writing more characters than the string contains.

Really your write() function should probably look more like:

void createTextFile()
{
    std::vector<std::string> vetor(10000, "teeeeeeeeeeeeeeeeeeeeeeest");
    std::ofstream file("text.data");

    for(size_t n = 0; n < vetor.size(); n += 5)
    {
        vetor[n] = "here";
    }

    for(auto& itr : vetor)
        file << itr << std::endl;
}

[lazpeng]

Hi

I'm not sure how exactly std::vector stores its data, but that method of writing its contents looks really bad

changing line 7 to
for(size_t i = 0; i < vetor.size(); i++) file << vetor[i] << '\n';
works fine

you should never assume anything about any data structure or class provided by an external library (i.e. which you didn't write), since it may change depending on the platform or version, use the provided interfaces and functions.

I'm sure there is better ways to write to a file, mostly for performance reasons, but for a little test the above one works just fine.

Hope it helps :)

[Chervil]

There's also a problem with the while loop in function readTextFile().

void readTextFile(){
    std::vector<std::string> vetor;
    std::string line;
    std::ifstream file("text.data");
    int n = 0;
    int m = 0;
    while (file.good()){
        std::getline(file, line);
        if (line.find("here")!=std::string::npos) {
            n++;
  //          std::cout << "found " << n << std::endl;
        }
        else
            m++;
    }
    std::cout << "n = " << n << "    m = " << m << '\n';
}

I temporarily commented out line 11 - purely to reduce the quantity of output generated.
Here is the output (assuming the file generate problem has been corrected as mentioned above):

n = 2000    m = 8001

Notice the second value is 8001 but it should be 8000 (so that m + n == 10000).

The problem is, the loop condition file.good() says what happened to the previous read. It does not predict whether the next getline will succeed.

Instead put the read operation as the loop condition, that way the body of the loop is processed only after a successful read :

    while (std::getline(file, line)) {
        if (line.find("here")!=std::string::npos) {
            n++;
  //          std::cout << "found " << n << std::endl;
        }
        else
            m++;
    }

[Enoizat]

#include <fstream>
#include <iostream>
#include <limits>
#include <string>
#include <vector>


void createTextFile(std::string& str);
std::vector<std::string>& readTextFile(std::ifstream& file, 
                                       std::vector<std::string>& phrases);
void waitForEnter();


int main()
{
    std::string filename("data.txt");
    createTextFile(filename);
    std::ifstream infile(filename);
    std::vector<std::string> phrases;
    readTextFile(infile, phrases);
    for(const auto& phrase : phrases) { std::cout << phrase << '\n'; }
    infile.close();
    waitForEnter();
    return 0;
}


void createTextFile(std::string& str)
{
    std::ofstream outfile(str);
    std::vector<std::string> vetor(10, "teeeeeeeeeeeeeeeeeeeeeeest");
    for(size_t i{}; i<vetor.size(); i++) {
        outfile << "phrase " << i << ": " << vetor.at(i) << '\n';
    }
}


std::vector<std::string>& readTextFile(std::ifstream& file, 
                                       std::vector<std::string>& phrases)
{
    std::string tmp;
    while(std::getline(file, tmp)) { phrases.push_back(tmp); }
    return phrases;
}


void waitForEnter()
{
    std::cout << "\nPress ENTER to continue...\n";
    std::cin.ignore(std::numeric_limits<std::streamsize>::max(), '\n');
}

[Stauricus]

oh, now i see why the text file wasn't human readable. thanks everybody for the answers, its working now :)