how to write binary file without deleting its previous contents

[dinesh999lama]

I am writing a binary file like this:

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?

[2kaud]

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