istringsteam with line breaks

Question

Okay I read that if we have a string s =" 1 2 3"

we can do :

istringstream iss(s);  
int a;
int b;
int c;

iss >> a >> b >> c;

Lets say we have a text file with the following :

test1
100 ms

test2
200 ms

test3
300 ms

ifstream in ("test.txt")
string s;
while (getline(in, s))
{
       // I want to store the integers only to a b and c, How ?
}

score 0 · Answer 1 · answered Jan 31 '15 at 19:09

0

1) You can rely on succesful convertions to int:

int value;
std::string buffer;
while(std::getline(iss, buffer,' ')) 
{
    if(std::istringstream(buffer) >> value)
    {
        std::cout << value << std::endl;
    }
}

2) or just skip over unnecessary data:

int value;
std::string buffer;
while(iss >> buffer) 
{
    iss >> value >> buffer;
    std::cout << value << std::endl;
}

answered Jan 31 '15 at 19:09

Alexey Andronov

582
6
28

1st method prints the integer values successfully but how to parse them to int a , int b and int c since they are only stored in "int value" as per the code ! – Tharwat Harakeh Jan 31 '15 at 19:57
@TharwatHarakeh, you can store them in dynamic array `std::vector v;` and instead of `std::cout << value << std::endl;` write `v.push_back(value)`. And after that, if you wish: `int a = v[0], b = v[1], c = v[2];` – Alexey Andronov Jan 31 '15 at 20:04
can u please provide a full working code for it ? i tried what u said but i can't make it work – Tharwat Harakeh Jan 31 '15 at 21:40
Code : http://pastebin.com/53LuYVGN and here is the error http://prntscr.com/5zo41l – Tharwat Harakeh Feb 01 '15 at 09:38
looks like your input file have less than 3 integers, and when you try to call `v[2]`, for example, there is no such element – Alexey Andronov Feb 01 '15 at 10:16
the file content is exactly the same as in the main post – Tharwat Harakeh Feb 01 '15 at 11:31
use step-by-step debugger feature to find out what's wrong – Alexey Andronov Feb 01 '15 at 11:35
@TharwatHarakeh, oh, you pass path as a sting, not the file argument. [Here](http://www.cplusplus.com/reference/fstream/ifstream/open/)'s how to open file properly – Alexey Andronov Feb 01 '15 at 15:01

score 0 · Answer 2 · answered Jan 31 '15 at 19:11

If you know the pattern of the details in the text file, you could parse through all the details, but only store the int values. For example:

ifstream in ("test.txt")
string s;
while (getline(in, s))
{
     getline(in,s); //read the line after 'test'.
     string temp;
     istringstream strm(s);
     s >> temp;
     int a = stoi(temp) // assuming you are using C++11. Else, atoi(temp.c_str())
     s >> temp;
     getline(in,s); // for the line with blank space
}

This above code is still somewhat of a inelegant hack. What you could do besides this is use random file operations in C++. They allow you to move your pointer for reading data from a file. Refer to this link for more information: http://www.learncpp.com/cpp-tutorial/137-random-file-io/

PS: I haven't run this code on my system, but I guess it should work. The second method works for sure as I have used it before.

istringsteam with line breaks

2 Answers2