wc can not count very large file

[pwu]

I have tried to calculate how many lines in our project.  In one 
directory it give me the value is 160k, but the total number for all
directories are only 50k.
my command is like this:
find . -name '*.[ch]' |xargs wc
The newlines are only 50K. I have about 20 directories, each has 100k to 
300k lines. I guess it is because wc use int not long to calculate
the lines and bytes


Thanks,
ping