As ILOG CPLEX is working, it can record messages to a log file. By default, the Interactive Optimizer creates the log file in the directory where it is running, and it names the file cplex.log. If such a file already exists, ILOG CPLEX adds a line indicating the current time and date and then appends new information to the end of the existing file. That is, it does not overwrite the file, and it distinguishes different sessions within the log file. By default, there is no log file for Component Library applications.

You can locate the log file where you like, and you can rename it. Some users, for example, like to create a specifically named log file for each session. Also you can close the log file in case you do not want ILOG CPLEX to record messages to its default log file.

The following sections show you the commands for creating, renaming, relocating, and closing a log file.

• In the Interactive Optimizer, use the command set logfile filename, substituting the name you prefer for the log file. In other words, use this command to rename or relocate the default log file.
• From the Callable Library, first use the routine CPXfopen() to open the target file; then use the routine CPXsetlogfile(). The ILOG CPLEX Reference Manual documents both routines.
• From Concert, use the setOut() method to send logging output to the specified output stream.

• If you do not want ILOG CPLEX to record messages in a log file, then you can close the log file from the Interactive Optimizer with the command set logfile *.
• By default, routines from the Callable Library do not write to a log file. However, if you want to close a log file that you created by a call to CPXsetlogfile(), call CPXsetlogfile() again, and this time, pass a NULL pointer as its second argument.
• From Concert, use the setOut() method with env.getNullStream() as argument, where env is an IloEnv object, to stop sending logging output to an output stream.