I don't have a Solaris or AIX machine to check, but the Linux man page for fopen says that r+ (+<) and w+ (+>) open the file and position the stream at the beginning of the file, while a+ (+>>) positions the stream at the end of the file. So your options are either to open with +>> and then seek to the beginning of the file before reading, or open with +<, read, and then seek to the end of the file before writing (although you will probably end up at the end of the file anyway, if you read the entire contents).