How to overwrite a file in C?

Question

I am trying to overwrite the contents of a FILE in C. Currently I have:

FILE* file  = fopen("filename.txt",  "r+");
fprintf(file, "%d", 1); // regardless of what's in the file, i want to clear it and put 1 in there
...
// legacy code somewhere else in the code base. can't change.
rewind(file);
fprintf(file, "%d", 2);
fflush(file);

However, this will not work properly. The result will be:

1, 21

Each subsequent number will be written to the beginning of the 1. For example:

1, 21, 31, 41, ...

I would like to know if there is a way to always overwrite what's in the file so the following is produced:

1, 2, 3, 4, ...

Any assistance would be appreciated.

Thank you.

EDIT:

I have changed the code to:

FILE* file  = fopen("filename.txt",  "w+");

The problem still persists.

Answer 1

You decide that in fopen. Just use "w" or "w+" instead of "r+".