how to write binary file without deleting its previous contents

I am writing a binary file like this:

Code:

---

const int sized = 300000000ULL;
int ad[sized];
...
ad[i] = some value;
...
            FILE* pFile;
            pFile = fopen("obj_pattern.bin", "wb");
            fwrite(ad, 1, sized*sizeof(int), pFile);
            fclose(pFile);

---

Now how can i again write given binary file obj_pattern.bin with some new values of ad[i] in another program. For example in first program i put ad[] values in the file as 1,2 now how can i again write that same file without deleting the previous saved values 1 and 2?

Mode "wb" will delete any existing contents. If you open the file as mode "ab", this will append the data to the existing contents. There is also mode "a+b" which will allow reading from the file at a specified position but writing to the end of the file. If you use mode "r+b" then you can position the file pointer to the end of the file before you write but the file must exist.

See https://msdn.microsoft.com/en-us/library/yeby3zcb.aspx