How to Read Numerical Data from a Text File in C ?

Reading Numerical Data from a Text File in C

Problem:

Consider a text file containing numerical data, such as:

45.78   67.90   87
34.89   346     0.98

How can we read this file in C and assign each number to a variable?

Solution:

Case 1: Reading a Limited Number of Values

If the number of values in the file is known, we can chain the >> operator to read values sequentially:

int main() {
  float a, b, c, d, e, f;
  ifstream myfile("data.txt");
  myfile >> a >> b >> c >> d >> e >> f;
  cout << a << "\t" << b << "\t" << c << "\t" << d << "\t" << e << "\t" << f << "\n";
  myfile.close();
  return 0;
}

Case 2: Reading an Unknown Number of Values

If the number of values is unknown, we can use a loop:

int main() {
  float a;
  ifstream myfile("data.txt");
  while (myfile >> a) {
    cout << a << " ";
  }
  myfile.close();
  return 0;
}

Case 3: Skipping Values

To skip a certain number of values in the file, use the following technique:

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

This code skips the first 1233 values and reads the 1234th value into the value variable.

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