C++ I/O Readable

Question

C++ I/O Readable

Sid Kraft 46

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?

0 comments

2 answers

Your answer

Answer 1

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.

Answer 2

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

Key issues:

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';

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");
```

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;
   }

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: