It is possible to read and write a file of parameter settings with the Callable Library. This kind of file is known as a PRM file. The file extension for a PRM file is .prm. The Callable Library routine CPXreadcopyparam reads parameter values from a file with the .prm extension. The routine CPXwriteparam writes a file of the current non-default parameter settings to a file with the .prm extension. Here is the format of such a file:

CPLEX Parameter File Version <number>
  <parameter_name>   <parameter_value>

ILOG CPLEX reads the entire file before changing any of the parameter settings. After successfully reading a parameter file, the Callable Library first sets all parameters to their default value. Then it applies the settings it read in the parameter file. No changes are made if the parameter file contains errors, such as missing or illegal values. There is no checking for duplicate entries in the file. In the case of duplicate entries, the last setting in the file is applied.

When you write a parameter file from the Callable Library, only the non-default values are written to the file. String values may be double-quoted or not, but are always written with double quotation marks.

The comment character in a parameter file is #. ILOG CPLEX ignores the rest of the line.

The Callable Library issues a warning if the version recorded in the parameter file does not match the version of the product. A warming is also issued of a non-integral value is given for an integer-valued parameter.

Here is an example of such a file:

CPLEX Parameter File Version 9.0
CPX_PARAM_EPPER                  3.45000000000000e-06
CPX_PARAM_IISIND                 1
CPX_PARAM_OBJULIM                1.23456789012345e+05
CPX_PARAM_PERIND                 1
CPX_PARAM_SCRIND                 1
CPX_PARAM_WORKDIR                "tmp"