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.
You can use conversion characters as part of the filename.
If the filename string is NULL, the default filename is restored. This is typically %v.pcv (the program name followed by the .pcv extension), or, if you are using the -view-file-format option to save data to Windows-format .cfy files, %v%p%n.cfy. If you specify a filename in the -counts-file option, it is this name that is restored.
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.