GCC errors out on code that used to work fine - filenames

Question

I have a program that has successfully compiled in the past, but now I get a bunch of errors.The source code is just:
#include <stdio.h>
#include <sys/types.h>
#include <sys/stat.h>
int main()
{
int fd;
fd = creat("datafile.dat", S_IREAD | S_IWRITE);
if (fd == -1)
printf("Error in opening datafile.dat\n");
else
{
printf("datafile.dat opened for read/write access\n");
printf("datafile.dat is currently empty\n");
}
close(fd);
exit (0);
}
Now I get the errors:
cre.C:8:54: error: ‘creat’ was not declared in this scope
cre.C:16:17: error: ‘close’ was not declared in this scope
cre.C:17:16: error: ‘exit’ was not declared in this scope
Sometimes I get an error about gxx_personality_v0 instead, and sometimes I get no error at all! I've tried updating gcc, but the problem remains. What's going wrong?
OS UBUNTU 12.1 on vaio laptop

Answer 1

From your error messages I see that you called your file cre.C. gcc is case-sensitive for file names: try naming it cre.c and compiling it.
$ LANG=C cc -o foo foo.C
foo.C: In function 'int main()':
foo.C:8:54: error: 'creat' was not declared in this scope
foo.C:16:17: error: 'close' was not declared in this scope
foo.C:17:16: error: 'exit' was not declared in this scope
but
$ LANG=C cc -o foo foo.c
foo.c: In function 'main':
foo.c:17:9: warning: incompatible implicit declaration of built-in function 'exit' [enabled by default]
As noted in a comment, a file with .C extension is handled by the C++ compiler, thus you are seeing those errors.

Answer 2

Read the man pages for the creat, close, and exit functions.
On my system, creat() requires:
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
close() requires:
#include <unistd.h>
and exit() requires:
#include <stdlib.h>
As for why the code was compiling before, it's hard to tell. Perhaps the compiler was being invoked in a more permissive mode that didn't complain about missing function declarations, or perhaps some of the headers you do include have #include directives for the headers you need.