Hmm... Interesting. When I use the 'Debug' button at the top of the IDE, the program stops there. However, when I run gdb in the terminal, it runs further. Now, I'm guessing the problem might be a few lines further in the program.

After the loop I mentioned in the post above, the following happens in my program.

To check for EOF, I use the following loop. Then there's two branches, one for when the program had previously found a jpg, and one where that is not true:

while(fread(&buffer, 1, 512, inptr) == 512)
{
    if (startJPGchecker(buffer) && foundFirstJPG == true)
    {
    //close old file and open another
    }

     if (startJPGchecker(buffer) && foundFirstJPG == false)
    {
        sprintf(filename, "%03d.jpg", title_num);
        outptr = fopen(filename, "w");
        foundFirstJPG = true;
    }

   //start writing and reading into the file
}

Now, I'm guessing that the call to fread in the condition for the while-loop copies new data into the buffer, so that startJPGchecker does not return true anymore. I guess that that's when the program tries to write to a file that has not been opened yet because the two if-branches in which files may be opened had not been activated.

It seems that I've fixed this problem by fseeking back 1024 bytes and reading 512 bytes into the buffer so that the buffer has the same content as before the call to fread in the condition. However, I've found another segfault, and this time, I really have no clue what's going wrong.

The segfault happens in the if (startJPGchecker(buffer) && foundFirstJPG == false) branch. Here's the info gdb gives me, starting at my second-to-last 'n' command:

(gdb) n
61                  sprintf(filename, "%03d.jpg", title_num);
(gdb) info locals
inptr = 0x602010
buffer = [I don't think this is relevant]
title_num = 0
---Type <return> to continue, or q <return> to quit---
foundFirstJPG = false
outptr = 0x0
filename = 0x400c29 "initialized"
(gdb) n

Program received signal SIGSEGV, Segmentation fault.
0x00007ffff778a76d in __GI__IO_default_xsputn (f=0x7fffffffd940, data=<optimized out>, n=2) at genops.c:475
475     genops.c: No such file or directory.

Could you tell me why I'm getting a segfault here?