how to write a structure in a shared mem segment.

[wysota]

Did you check that the shared segment got updated? For example by printf()ing the data directly from within the shared segment.

[nass]

isnt it sufficient looking directly at the associated file on the disk?
cause as soon as i save, i can see changes on the file... so i figure i save in the shared memory and directly the file on the disk is updated. causei surely dont write to the file.. i just 'save' to a location pointed to by the file_memory pointer (+ the offset)
nass

[wysota]

isnt it sufficient looking directly at the associated file on the disk?

If it seems that the segment is not updated, then it's better to check that out. There is no reason why the assignment should fail, so if it fails, there is a reason to suspect that the segment wasn't updated.