Difference between r+ and w+ in fopen()

Question

In fopen("myfile", "r+") what is the difference between the "r+" and "w+" open mode? I read this:

"r" Open a text file for reading.
"w" Open a text file for writing, truncating an an existing file to zero length, or creating the file if it does not exist.

"r+" Open a text file for update (that is, for both reading and writing).
"w+" Open a text file for update (reading and writing), first truncating the file to zero length if it exists or creating the file if it does not exist.

I mean the difference is that if I open the file with "w+", the file will be erased first?

Answer 1

Both r+ and w+ can read and write to a file. However, r+ doesn't delete the content of the file and doesn't create a new file if such file doesn't exist, whereas w+ deletes the content of the file and creates it if it doesn't exist.

Answer 2

The main difference is w+ truncate the file to zero length if it exists or create a new file if it doesn't. While r+ neither deletes the content nor create a new file if it doesn't exist.

Try these codes and you will understand:

#include <stdio.h> int main() {    FILE *fp;     fp = fopen("test.txt", "w+");    fprintf(fp, "This is testing for fprintf...\n");    fputs("This is testing for fputs...\n", fp);    fclose(fp); }   

and then this

#include <stdio.h> int main() {    FILE *fp;     fp = fopen("test.txt", "w+");    fclose(fp); }    

If you will open test.txt, you will see that all data written by the first program has been erased.
Repeat this for r+ and see the result.
Here is the summary of different file modes (1 => ture, 0 => false):