Removing and renaming files with C error - c

Question

So i'm trying updating data from original file to a new temporary file, then i remove the original file and rename the temp file with the name of the original one like this:
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <time.h>
int main(){
FILE * fptr = NULL;
FILE * temp;
fptr = fopen("Original.txt", "rw+");
temp = fopen("temp.txt", "w");
if(fptr==NULL)//Check if file was opened successfully
{
printf("File could not be opened");
}
//cicle of me adding data to temp file
fclose(fptr);
fclose(temp);
remove("Original.txt");
rename("temp.txt","Original.txt");
return 0;
}
it works the first time, but when i execute again the Original.txt ends up blank. What can be causing that?
I've tried changing temp = fopen("temp.txt", "w"); to temp = fopen("temp.txt", "ab+"); but the info of Original.txt ends up with no spaces or new lines between (all together). And same with "wb"
"rb" the Original.txt file disappears.
if necessary ill add the entire code, althought i dont think its revelant

Answer 1

The moment you do an fopen (path, "w") it truncates the file pointed by the path. Then you close the file. Therefore essentially, your "temp.txt" is an empty file after the line fclose (temp). Get rid of the "w+" and "w" as they will truncate the file (make it zero length).
See man fopen
w Truncate file to zero length or create text file for writing.
The stream is positioned at the beginning of the file.
w+ Open for reading and writing. The file is created if it does not exist, otherwise it is truncated. The stream is positioned
at the beginning of the file.
You do not need to open and or close the file at all. If you see the remove and rename uses absolutely nothing from the previous part of the code. Also check man rename and man remove. If you want to know if the files are present of not. Check the return values of these functions. In case of error, you can always inspect the errno to understand what exactly went wrong. (See manpage for details).

Answer 2

Not sure what you are trying to do exactly, but depending on your question, you need only "r" mode for reading.
i.e, fptr = fopen("Original.txt", "r");
Additionally, couple of suggestions, but not answer to your question:
You are checking fptr == NULL, but proceeding to write data anyway? what if fptr == NULL is true and you try to read from a NULL pointer? Besides putting an error message, put a return -1 or something so that the program does not continue further for that case.
You should check temp == NULL as well, to detect whether file is opened for writing also. What if temp == NULL is true and you try to write to a NULL pointer?