C++ I/O Readable

Question

Not sure what I am doing wrong but this should output readable values, does not:

#include fstream;

float PLOTX[20];

float PLOTY[20];

float PLOTZ[20];

int INOW=20;

I = 0;

//Open the output file for writing

ofstream out("C:/Plot Data");

do

{

 cout << PLOTX[I] << ' ' << PLOTY[I] << ' ' << PLOTZ[I];

 ++I;

} while (I <= INOW);

//Close the file

out.close();

When I review "c/Plot File" is empty?

Answer 1

The file is empty because the code never writes anything to the ofstream and the loop bounds are off.

Key issues:

1. No output to the file stream
   The loop writes only to cout:

      cout << PLOTX[I] << ' ' << PLOTY[I] << ' ' << PLOTZ[I];
   

   but never to out. To write to the file, use out:

      out << PLOTX[I] << ' ' << PLOTY[I] << ' ' << PLOTZ[I] << '\n';
   

2. Incorrect include and file name
   • The include should be:

          #include <fstream>
     

     not #include fstream;.
   • The file path should include an extension and use consistent slashes, for example:

          ofstream out("C:/Plot Data.txt");
     

3. Loop goes out of bounds
   float PLOTX[20]; defines indices 0 to 19.
   int INOW = 20; and

      I = 0;
      do {
          ...
          ++I;
      } while (I <= INOW);
   

   will access PLOTX[20] on the last iteration, which is out of range and undefined behavior. Use < and match the array size:

      int INOW = 20;   // number of valid points
      int I = 0;
      while (I < INOW) {
          out << PLOTX[I] << ' ' << PLOTY[I] << ' ' << PLOTZ[I] << '\n';
          ++I;
      }
   

4. Optional: check for file open errors
   Before writing, verify the stream is good:

      ofstream out("C:/Plot Data.txt");
      if (out.fail()) {
          // handle error: path invalid, no permission, etc.
          return 1;
      }
   

Putting it together:

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

float PLOTX[20];
float PLOTY[20];
float PLOTZ[20];

int main() {
    int INOW = 20;   // number of points

    ofstream out("C:/Plot Data.txt");
    if (out.fail()) {
        cout << "Failed to open output file" << endl;
        return 1;
    }

    for (int I = 0; I < INOW; ++I) {
        out << PLOTX[I] << ' ' << PLOTY[I] << ' ' << PLOTZ[I] << '\n';
    }

    out.close();
}

This will produce a text file with readable values.

---

References:

• Output File Stream Member Functions
• Binary Output Files
• Input Stream Member Functions
• Input and output
• Controlling streams

Answer 2

You should also learn naming conventions for c/c++.

• class and type names Pascal case
• Variables and function names camel case or snake case
• Macro or constants names all upper case
• Global variables prefixed with g_

Answer 3

Hello @Sid Kraft ,

Thanks for your question.

Your file is empty because:

• Use out instead of cout to write to the file.
• Change I <= INOW to I < INOW to avoid accessing element 20 in a 20-element array.
• There are some minor syntax mistakes::
  • #include <fstream>
  • int I = 0;

You can refer to the following code example:

#include <iostream>
#include <fstream>

int main() {
    float PLOTX[20] = {0};
    float PLOTY[20] = {0};
    float PLOTZ[20] = {0};

    int INOW = 20;
    int I = 0;

    std::ofstream out("C:/PlotData.txt");

    do {
        out << PLOTX[I] << ' ' << PLOTY[I] << ' ' << PLOTZ[I] << '\n';
        ++I;
    } while (I < INOW);

    out.close();
    return 0;
}

I hope this addresses your question. If this response was helpful, please consider following the guidance to provide feedback. Thank you.