append « pointer « C File Q&A

1. Appending a data to file in c    stackoverflow.com

I require to add a string before 45byte in an existing file. I tried using fseek as bellow.

int main()
{
 FILE *fp;
 char str[] = "test";     

 fp ...

2. When opening a file in append mode, how can I reposition the file pointer?    stackoverflow.com

I am trying to insert some data into the middle of a file. I have opened the file in append mode as:

file = fopen(msg->header.filename, "ab");

3. Does fseek() move the file pointer to the beginning of the file if it was opened in "a+b" mode?    stackoverflow.com

I wish to open a file using the "a+b" mode, i.e. if it does not exist it is created automatically, but if it does I don't want to overwrite it. I ...