undefined reference to `fwrite'

[Altera_Forum]

Hi all, 

 We got this error if we use the (small) Newlib C library: -- start -- Error pure.o * In function `__cxa_pure_virtual': undefined reference to `fwrite' pact_sb line 0 -- end  FYI: we do remove/comment all printf statements  How can we get rid of this error? Any one helps?  Regards,  Kwok Wong

[Altera_Forum]

--- Quote Start ---  originally posted by kwokwong@Dec 29 2004, 10:51 AM hi all,  we got this error if we use  the (small) newlib  c library: -- start -- error  pure.o * in function `__cxa_pure_virtual&#39;:  undefined reference to `fwrite&#39; pact_sb  line 0 -- end  fyi:  we do remove/comment all printf statements  how can we get rid of this error? any one helps?  regards,  kwok wong  --- Quote End ---   The reference is made in the file pure.cc:  --start --# ifdef _GLIBCPP_HAVE_UNISTD_H# include <unistd.h># define writestr(str) write(2, str, sizeof(str) - 1)# ifdef __GNU_LIBRARY__  /* Avoid forcing the library&#39;s meaning of `write&#39; on the user program  by using the "internal" name (for use within the library). */ /*# define write(fd, buf, n) __write((fd), (buf), (n))*/# endif# else# include <cstdio># define writestr(str) std::fputs(str, stderr)# endif  extern "C" void __cxa_pure_virtual (void) {  writestr ("pure virtual method called\n");  std::terminate (); } -- end  Who can tell what this funtions does and/or which ohter (libray) funtion requires this functions?

[Altera_Forum]

The function __cxa_pure_virtual() is a placeholder function inserted automatically by the compiler. It is used whenever you declare a pure virtual function in a base class (that is, a function that won&#39;t have an implementation provided: 

 class an_abstract_base_class {    virtual void do_something() = 0; }  Since you can&#39;t create instances of an_abstract_base_class, you shouldn&#39;t be able to call the non-existant function an_abstract_base_class::do_something(). The compiler still needs to create a vtable (virtual function dispatch table) for abstract classes (those with one or more pure virutal methods like an_abstract_base_class), so it has to put something in the vtable entries corresponding to pure virtual functions: it uses __cxa_pure_virtual(). In properly written code __cxa_pure_virtual() should never get called. If it does somehow get called it&#39;s a signal that something has gone seriously wrong with your code.  So, to eliminate the undefined reference error you have two choices: Either remove all pure virtual functions from you project, or provide your own version of __cxa_pure_virtual() that doesn&#39;t use facilities which aren&#39;t available on your hardware platform (e.g. just go into an infinite loop flashing an LED).

[Altera_Forum]

Thanks for the reply. 

I&#39;ll look for all unimplemented pure virtual methods.