Example: Callable Library Message Channels

ILOG CPLEX 11.0 User's Manual > Programming Considerations > Managing Input and Output > Controlling Message Channels > Example: Callable Library Message Channels

Example: Callable Library Message Channels

INDEX

PREVIOUS NEXT

This example shows you how to use the ILOG CPLEX message handler from the Callable Library. It captures all messages generated by ILOG CPLEX and displays them on screen along with a label indicating which channel sent the message. It also creates a user channel to receive output generated by the program itself. The user channel accepts user-generated messages, displays them on screen with a label, and records them in a file without the label.

The complete program lpex5.c appears online in the standard distribution at yourCPLEXinstallation/examples/src. This example derives from lpex1.c, a program in the ILOG CPLEX Getting Started manual. There are a few differences between the two examples:

In this example, the function ourmsgfunc (rather than the C functions printf or fprintf(stderr, . . .)) manages all output. The program itself or CPXmsg from the ILOG CPLEX Callable Library calls ourmsgfunc. In fact, CPXmsg is a replacement for printf, allowing a message to appear in more than one place, for example, both on screen and in a file.

Only after you initialize the ILOG CPLEX environment by calling CPXopenCPLEX can you call CPXmsg. And only after you call CPXgetchannels can you use the default ILOG CPLEX channels. Therefore, calls to ourmsgfunc print directly any messages that occur before the program gets the address of cpxerror (a channel). After a call to CPXgetchannels gets the address of cpxerror, and after a call to CPXaddfuncdest associates the message function ourmsgfunc with cpxerror, then error messages are generated by calls to CPXmsg.

After the TERMINATE: label, any error must be generated with care in case the error message function has not been set up properly. Thus, ourmsgfunc is also called directly to generate any error messages there.

A call to the ILOG CPLEX Callable Library routine CPXaddchannel initializes the channel ourchannel. The Callable Library routine fopen opens the file lpex5.out to accept solution information. A call to the ILOG CPLEX Callable Library routine CPXaddfpdest associates that file with that channel. Solution information is also displayed on screen since ourmsgfunc is associated with that new channel, too. Thus in the loops near the end of main, when the solution is printed, only one call to CPXmsg suffices to put the output both on screen and into the file. A call to CPXdelchannel deletes ourchannel.
Although CPXcloseCPLEX will automatically delete file- and function-destinations for channels, it is a good practice to call CPXdelfpdest and CPXdelfuncdest at the end of your programs.

PREVIOUS NEXT