从文件读取数据到单独的Int值

Question

I am looking to take in data values from a file and store them in separate integer variables. I have the following variables:

int r;
int c;
int startR;
int startC;

The file provides the values in the form:

2 32 12 4

These are just examples and I need to store these four values in the variables. I am using the getline function to get the line and then calling a split function to take the string and split it and put it into the four values.

getline(fileName, line);
split(line);

void split(string l)
{
  //this is where I am struggling to find the best way to get the values stored in the ints
}

Answer 1

Read straight from the file into your variables.

#include <iostream>
#include <fstream>
using namespace std;

int main() {
    std::ifstream file("test.txt");
    int a, b, c, d;
    if (file.is_open()) {
        cout << "Failed to open file" << endl;
        return 1;
    }
    if (file >> a >> b >> c >> d) { // Read succesfull
        cout << a << " " << b << " " << c << " " << d << endl;
    }
    return 0;
}

Answer 2

If you are still having problems parsing the information from the file, you can take a very simple approach -- continuing with your getline beginning to then create a stringstream object from line that will allow you to use the operator making sequential calls to get each next value from your line. For example:

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

int main (void) {

    int r, c, startR, startC;           /* variable declarations */
    std::string fname, str;

    std::cout << "Enter a filename: ";  /* prompt for filename */
    std::cin >> fname;

    std::ifstream f (fname);            /* open file */
    if (!f.is_open()) {                 /* validate open for reading */
        std::cerr << "error: file open failed\n";
        return 1;
    }
    std::getline (f, str);              /* read line into str */

    std::stringstream s (str);          /* create stringstream s with str */
    s >> r >> c >> startR >> startC;    /* parse data */

    /* output parsed data for confirmation */
    std::cout << "r: " << r << "  c: " << c << "  startR: " << startR 
            << "  startC: " << startC << "\n";

    f.close();                          /* close file */

    return 0;
}

Example Input File

$ cat dat/4nums.txt
2 32 12 4

Example Use/Output

$ ./bin/strstreamtst
Enter a filename: dat/4nums.txt
r: 2  c: 32  startR: 12  startC: 4

Look things over and let me know if you have further questions.

Answer 3

You can try something like this.

FILE* in = NULL;
int r;
int c;
int startR;
int startC;

errno_t fin = freopen_s(&in, "input.txt", "r", stdin);
assert(0x0 == fin);
cin >> r >> c >> startR >> startC;

Here with freopen(), "cin" will read data values from file rather than from standard input.

Answer 4

Your just need to store the value into the appropriate variable.

See this for more information.