How do you read 6 characters from a file at a time?

[ashleygarrott]

Hey guys, I'm writing from my fresh new account. I'm a beginner so please, excuse my ignorance. I would like to read 6 bytes at a time from a text file using ifstream. For example, the file contains this information:

  73647364863242384625347632543243434234234

I want to read the first 6 numbers, then the second 6, and so on. Anyone care to help me on that?

[Yay295]

http://www.cplusplus.com/reference/istream/istream/get/

or

http://www.cplusplus.com/reference/istream/istream/getline/

They can be used to do the same thing. The only difference being getline removes the delimiter if it finds it, get just stops getting.

[ashleygarrott]

It always says no matching member function for call to get when I try to use it. That is why I didn't. How do I fix that?

[Chervil]

I'v been getting this message since forever "no matching member function for call to get". That's why I couldn't use it.

The reason why you couldn't use it was probably because the wrong parameters were specified. You'd need to show the actual code which didn't work for a more detailed explanation.

[ashleygarrott]

I kind of know my mistake now :P However, this

ifstream infile;
word=infile.get()

will read the next character in the file right? How do I make it read 6 characters? (specifically, 6 numbers in a sequence of numbers).

[ashleygarrott]

Hey guys, thanks a lot for your help, I used Yay295's advise and used the get function. I looped it to get 6 characters and saved them in an array, then converted it into an int. Again, thanks a lot.

[Chervil]

You could do that without a loop. Just specify the number of characters in the call.
The example on the reference page shows how to read 255 characters into a buffer. Just change 256 to 7.

#include <iostream>
#include <fstream>
#include <cstdlib>

using namespace std;

int main()
{
    ifstream fin("input.txt");
    
    char buf[7];

    while (fin.get(buf, 7))
    {
        int numchars = fin.gcount(); // optional, see how many chars were read.
        int num = atoi(buf);
        
        cout << "length: " << numchars 
             << "  buf: "  << buf 
             << "  int: "  << num << endl;

    }    
  
} 

output:

length: 6  buf: 736473  int: 736473
length: 6  buf: 648632  int: 648632
length: 6  buf: 423846  int: 423846
length: 6  buf: 253476  int: 253476
length: 6  buf: 325432  int: 325432
length: 6  buf: 434342  int: 434342
length: 5  buf: 34234  int: 34234

[jlb]

You could also bypass the C-string and just use the extraction operator>> into a string, then use either a stringstream to process the string or something like stoi(), atoi().

#include <iostream>
#include <sstream>
#include <iomanip>

using namespace std;

int main()
{
std::string input = "73647364863242384625347632543243434234234";
std::string output;
int num;

std::istringstream ins(input);

while(ins >> setw(6) >> output) // Extract 6 characters from the stream.
{
std::istringstream sin(output);
sin >> num;
cout << "output:" << setw(7) << output
<< " length: " << output.length()
<< " num:" << setw(7) << num << endl;
}
}