How to read specific data from file into array string

Question

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How can I read data into three string array? first column into 1st string array, second column into 2nd string array, third column into 3rd string array. This is the code I tried, but the last array take into the line.

#include <iostream>
#include <string>
#include <sstream>
#include <fstream>

using namespace std;
 int main(){
    //load the text file and put it into a single string:
    std::ifstream in("test.txt");
    std::stringstream buffer;
    buffer << in.rdbuf();
    std::string test = buffer.str();
    std::cout << test << std::endl << std::endl;

//create variables that will act as "cursors". we'll take everything between them.
size_t pos1 = 0;
size_t pos2;

//create the array to store the strings.
std::string str[5];
std::string str2[5];
std::string str3[5];

int x;
int y;

for(y=0; y<5;y++){

    for ( x=0; x<3; x++){
        
        pos2 = test.find(" ", pos1); //search for the bar "|". pos2 will be where the bar was found.
    
       if(x==0){
       
        str[y] = test.substr(pos1, (pos2-pos1)); //make a substring, which is nothing more 
    
       }else if(x==1){
       
        str2[y] = test.substr(pos1, (pos2-pos1)); //make a substring, which is nothing more 
    
       
       }else if(x==2){
       
        str3[y] = test.substr(pos1, (pos2-pos1)); //make a substring, which is nothing more 
       
       }                                       //than a copy of a fragment of the big string.
      //  std::cout << str[x] << std::endl;
       // std::cout << "pos1:" << pos1 << ", pos2:" << pos2 << std::endl;
        pos1 = pos2+1; // sets pos1 to the next character after pos2. 
                         //so, it can start searching the next bar |.
    }
}

for (int p=0; p<5; p++){
    
    cout << str[p] <<endl;
    cout << str2[p] <<endl;
    cout << str3[p] <<endl;
}

    return 0;
 }

Why not use operator>> with the ifstream directly, do this in the for loop with index variable y in >> str[y] >> str2[y] >> str3[y]; — Some Guy
– Some Guy, Commented May 17, 2016 at 20:05

threaz · Accepted Answer · 2016-05-17 20:10:59Z

2

Putting the whole file in one string can be very inefficient if you consider really big files.

The goal you are trying to achieve isn't really that complicated as you'd expected(at least in c++). You can just do:

for(size_t ind = 0; ind < 5; ++ind)
    in >> str[ind] >> str2[ind] >> str3[ind];

answered May 17, 2016 at 20:10

threaz

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2 Comments

WJ LIM Over a year ago

yes, >> operator is simply efficient but what if my data got space between like a name:Adam Maxwell. I need to save the whole name in 1 string. But the >> operator will think Adam as 1 string, Maxwell be the another one.

threaz Over a year ago

To be clear: what is your delimiter? Is it space or "|" because both of them exist in your code?

Taha Tekdoğan · Accepted Answer · 2016-05-17 20:04:43Z

0

I tried it in a different way, let's understand the simple code below.

while(in.good())
{
string stri;
int i=1,a=0,b=0,c=0;
in >> stri;

switch(i%3) {
case 1:
str[a]=stri;
a++;
break;
case 2:
str2[b]=stri;
b++;
break;
case 3:
str3[c]=stri;
c++;
break;
}
i++;

}

Here variables a,b and c counts array index. Every loop, it calculates (i%3) and fills the correct array.

Code may have some issues, it is just for idea. I did not even test it.

NOTE THAT this code will work if and only if you have 3 columns.

answered May 17, 2016 at 20:04

Taha Tekdoğan

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