Reading space seperated txt file into arrays C++

Question

the problem that I am having is that I should read in the values 7 write 0x01 0x27 from my .txt file and the loop will only run 1 time, giving the output 0 - 7 1 0x01 0x27 (the 1 represents write, 0 = read, 2 = not set), but, the values that I have printed out with the print statement show the values as

0 - 7 1 0x30 0x78
1 - 1 2 0x00 0x00 //where the 2 is it reads in 0x27 as a string

So, I am trying to figure out why it is reading in extra values instead of just the ones in the file.

void ioLoad(char* name)
{   
    std::ifstream inF;
    inF.open(name, ios_base::in);
    int i = 0;
    string rw;
    while(!inF.eof()){
        inF >> var.time[i]; //int time, from struct 'var'
        inF >> rw;          //string rw, should read either read or write
        inF >> std::hex >> var.address[i] //unsigned char address, from struct 'var' >>PROBLEM LINE<<
        if (rw == "write")
        {
            var.state[i] = WRITE; //stores an enum value as the state
            inF >> std::hex >> var.value[i];  //unsigned char value, from struct 'var' >>PROBLEM LINE<< 
        }
        printf("%d - %d %d 0x%02X 0x%02X\n", i, var.time[i], var.state[i], var.address[i], var.value[i]);
        i++
    }
    inF.close()
}

any help would be greatly appreciated and if you need more information please let me know.

`inF.eof()` returns true if the last read operation hit the end of file, not whether the current read position is at the end of file. — Vaughn Cato, Apr 19 '20 at 16:53
Please post the actual code in [mcve]. The posted code does not correspond to the expected output format. — 273K, Apr 19 '20 at 17:28

score 0 · Answer 1 · answered Apr 19 '20 at 16:56

using .eof as the condition is a risky buissnes, as the guy commenthing on your post told you, eof runs till the last reading resulted in failure. that means the last action will run twice. here is a good post about this: Why is iostream::eof inside a loop condition (i.e. `while (!stream.eof())`) considered wrong?

there are other options like while(file >> data) or checking where is the end of the file and runing till there.

also note that if you are doing /n between each row of your input file you need to "take it" before you continue, otherwise your next reading action will take it instead of taking the text you want.

Thanks, I will take the eof() into consideration and probably change it. but, would that be affecting why it is reading in `0x30 0x78` instead of `0x01 0x27`. — amfila, Apr 19 '20 at 17:09

273K · Accepted Answer · 2020-04-19T17:42:48.177

var.address[i] and var.value[i] have type unsigned char. Your compiler treats chars as unsigned numerics. So the line inF >> std::hex >> var.address[i] reads chars. You could understand it just looking at the ASCII table.

When inF >> std::hex >> var.address[i] performed, the input is 0x01 and '0' is placed to, that is 0x30. When inF >> std::hex >> var.value[i]; performed, the input is x01 and 'x' is placed to, that is 0x78.

You can read into unsigned int tmp

unsigned tmp;
inF >> std::hex >> tmp;
var.address[i] = static_cast<unsigned char>(tmp);
if (rw == "write") {
  var.state[i] = WRITE;
  inF >> std::hex >> tmp;
  var.value[i] = static_cast<unsigned char>(tmp);
}

Reading space seperated txt file into arrays C++

2 Answers2