在C ++中从文件读取整数和字符

Question

So, i'm trying to write a program that can read data from a file. The file consists of integers, chars and doubles. And i have to be able to assign them to different variables for further calculation (this is actually just a part of a bigger program). I've searched around the web (here also), and i've seen different solutions. stringstream, vectors and whatnot. The one i got furthest with, was using "skipws" when reading. But i can't seem to read the integers properly.

I would prefer a solution that requires the use of as few methods (streams, gets etc) as possible. But if i need more, i can live with it.

#include <iostream>
#include <fstream>
#include <cstring>

using namespace::std;

int main()
{
    int j = 0, kill = 0, i;
    char initials[10];
    int results[10];
    double avg;

    ifstream read("P1.txt");

    if (!read) //test to see if file can be opened.
    {
        cerr << "Error" << endl;
        exit(1);
    }

    while(kill != 1) //kill = 1 same as eof. Just my weird way of coding. 
    {
        switch (j)
        {
            case 0:     //read the first line of data, which is the chars.
                read >> skipws >> initials;
                j++;
                break;

            case 1: //read the second line of data, which is 10 integers and whitespace
                for (i=0;i<10;i++)
                read >> skipws >> results[i];
                j++;
                break;

            case 2:     //read the last line which is a single double.
                read >> skipws >> avg;
                j++;
                break;

            case 3: //check for end of file. 
                if(read.eof() == 0)
                    kill = 1;
                break;
        }
    }
    //the 3 lines below are just writing the contents of the file to the prompt. 
    //It's to check that values are stored correctly for further use. 
    cout << initials << endl; 
    cout << results << endl;
    cout << avg << endl;

    return 0;
}

I know exactly what y input file, "P1.txt", will look like, because i create it myself in another part of the program. It looks like this:

ccs
2 4 5 3 1 4 6 1 1 1
2.8       

Those 3 lines gives me the initials of a player, his results of 10 games and his average score. In short, the data of one player. In the final program, i need to be able to read values for maybe 10 players.

I'm expecting the 3 cout lines in the end to show this:

ccs
2453146111
2.8

Now, this is as far as i have gotten. If i declare results[10] as char i can get this in my console:

ccs
2453146111ccs
2.8

If i declare it as int i get this

ccs
0x7fff5fbff6c0
2.8

Obviously, i can see that values aren't stored properly and something is out of hand, but i need another persons eyes on this. I'm out of clues.

I know this is a messy way to do it and that it can be done in less space, but i'm new to C++, so this made sense to me, and made it fairly easy for me to locate my mistakes, until now.

I tried to explain it as well as i could. This is my first post here, so please tell me if you need more info.

Thanks in advance!! Chris.

Answer 1

when results is int[10] and you make cout << results << endl it will print the array memory address you should make loop that print result[i] in each iteration.

for(i=0;i<10;i++){
      cout<< result[i]; 
}

and it will give the correct result

Answer 2

I would suggest the following if you are using C++:

• Create three stringstream s
• Read each line into one stringstream
• For each line use (when your stringstream is called ss ):
  • ss >> c (with c your character)
  • ss >> i (with i your integer)
  • ss >> d (with d your double)
• Put the values in a vector when more than one input can be given on a line.

Some code:

    string s[3] = {"ccs",
        "2 4 5 3 1 4 6 1 1 1",
        "2.8"
    };
    stringstream ss[3];

    /*
    Open file, get the first line into s[0], second into s[1] and third into s[2]
    */

    ss[0] << s[0];
    ss[1] << s[1];
    ss[2] << s[2];
    char c;
    int i;
    double d;

    vector<char> initials;
    vector<int> scores;
    vector<double> averages;

    while (ss[0] >> c) {
        cout << c << " ";
        initials.push_back(c);
    }
    cout << endl;
    while (ss[1] >> i) {
        cout << i << " ";
        scores.push_back(i);
    }
    cout << endl;
    while (ss[2] >> d) {
        cout << d << " ";
        averages.push_back(d);
    }
    cout << endl;

Answer 3

This problem is made significantly easier by the fact that your data takes a known format. Don't let this go to waste.

string initials;
vector<int> r(NUM_SCORES);
double avg;

Now to get the data:

ifstream infile;
infile.open(...);
while(infile >> initials){ // i.e. "while there's another player"
    for(int i=0; i<r.size(); i++) infile >> r.at(i);
    infile >> avg;
}

Job done.

cout << "Player " << intials << " scored:" << endl;
for(int i=0; i<r.size(); i++) cout << r.at(i);
cout << endl << "giving him an average of " << avg << endl;

Answer 4

Also when you read in a value from a file, it is not an "int" data type. you cannot just push it back to a array of int's and expect it to work, you will probably need to convert it to an int using something like std::stoi

Answer 5

Don't re-invent the wheel, you can use Boost::tokenizer to tokenize the string and use Lexical_cast to convert strings to numbers.

If you want to use plain c you can use strtok for tokenizing the string