Read Numeric Data from a Text File in C++

by

Repeat >> reads in loop.

#include <iostream>
#include <fstream>
int main(int argc, char * argv[])
{
    std::fstream myfile("D:\\data.txt", std::ios_base::in);

    float a;
    while (myfile >> a)
    {
        printf("%f ", a);
    }

    getchar();

    return 0;
}

Result:

45.779999 67.900002 87.000000 34.889999 346.000000 0.980000

If you know exactly, how many elements there are in a file, you can chain >> operator:

int main(int argc, char * argv[])
{
    std::fstream myfile("D:\\data.txt", std::ios_base::in);

    float a, b, c, d, e, f;

    myfile >> a >> b >> c >> d >> e >> f;

    printf("%f\t%f\t%f\t%f\t%f\t%f\n", a, b, c, d, e, f);

    getchar();

    return 0;
}

Edit: In response to your comments in main question.

You have two options.

  • You can run previous code in a loop (or two loops) and throw away a defined number of values – for example, if you need the value at point (97, 60), you have to skip 5996 (= 60 * 100 + 96) values and use the last one. This will work if you’re interested only in specified value.
  • You can load the data into an array – as Jerry Coffin sugested. He already gave you quite nice class, which will solve the problem. Alternatively, you can use simple array to store the data.

Edit: How to skip values in file

To choose the 1234th value, use the following code:

int skipped = 1233;
for (int i = 0; i < skipped; i++)
{
    float tmp;
    myfile >> tmp;
}
myfile >> value;

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