[Solved] How to read and write files using printf and scanf in C? [closed]

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You basically have three options.

Option I

Redirect stdin/stdout (those are the streams scanf reads from and printf writes to) in the console, when you start your program. On both Windows and Linux, this can be done like so:

  • < in.txt – redirects all reads from stdin to in.txt
  • > out.txt – redirects all writes to stdout to out.txt

You can combine these. For example, to have your program read from in.txt and write to out.txt, do this in the terminal (command line):
myprogram < in.txt > out.txt

Option 2

Again, you can redirect the standard streams, this time in your code, using freopen. For example:

freopen("out.txt", "w", stdout);
freopen("in.txt", "r", stdin);

The result will be exactly the same as above.

Option 3

Use C’s file I/O: first fopen, then fscanf and fprintf:

FILE* fIn, fOut;
fIn = fopen("in.txt", "r");
fOut = fopen("out.txt", "w");
// Here you should check if any of them returned NULL and act accordingly

You can then read and write like so:

fscanf(fIn, "%d %d", &x, &y);
fprintf(fOut, "Some result: %d\n", result);

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solved How to read and write files using printf and scanf in C? [closed]