Syntax: int purecov_set_filename (const char *filename)
This function sets the name of the file for saving or merging the accumulated counts when the program exits or executes another program. This call does not actually write data or clear the counts.
The filename is subject to expansion of conversion characters.
If the filename string is NULL, the default filename is restored. This is typically the name of the program with the .pcv extension (%v.pcv), unless you specify the -counts-file option.
If the filename is unqualified (contains no '/'), it is written in the directory where the program lives. A qualified filename can be either absolute or relative to the current working directory.