Thread: Compilation error with -O2 option in g++

Please suggest how can I get rid of error in following code

-------klip---------------------

Code:

#include <iostream>
#include <map>
#include <time.h>
#include <netinet/in.h> // For sockaddr_in
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>

using namespace std;

#define VAL() htonl(0x00FFFFFF)
const uint32_t AVP_LENGTH_VALUE = VAL();

int main()
{
}

-------klap--------------------

Compilation
----------klip------------------
$g++ -v  -O2  test.cxx
Using built-in specs.
Target: x86_64-redhat-linux
Configured with: ../configure --prefix=/usr --mandir=/usr/share/man --infodir=/usr/share/info --enable-shared --enable-threads=posix --enable-checking=release --with-system-zlib --enable-__cxa_atexit --disable-libunwind-exceptions --enable-libgcj-multifile --enable-languages=c,c++,objc,obj-c++,java,fortran,ada --enable-java-awt=gtk --disable-dssi --enable-plugin --with-java-home=/usr/lib/jvm/java-1.4.2-gcj-1.4.2.0/jre --with-cpu=generic --host=x86_64-redhat-linux
Thread model: posix
gcc version 4.1.2 20080704 (Red Hat 4.1.2-48)
 /usr/libexec/gcc/x86_64-redhat-linux/4.1.2/cc1plus -quiet -v -D_GNU_SOURCE test.cxx -quiet -dumpbase test.cxx -mtune=generic -auxbase test -O2 -version -o /tmp/cclvQAdT.s
ignoring nonexistent directory "/usr/lib/gcc/x86_64-redhat-linux/4.1.2/../../../../x86_64-redhat-linux/include"
#include "..." search starts here:
#include <...> search starts here:
 /usr/lib/gcc/x86_64-redhat-linux/4.1.2/../../../../include/c++/4.1.2
 /usr/lib/gcc/x86_64-redhat-linux/4.1.2/../../../../include/c++/4.1.2/x86_64-redhat-linux
 /usr/lib/gcc/x86_64-redhat-linux/4.1.2/../../../../include/c++/4.1.2/backward
 /usr/local/include
 /usr/lib/gcc/x86_64-redhat-linux/4.1.2/include
 /usr/include
End of search list.
GNU C++ version 4.1.2 20080704 (Red Hat 4.1.2-48) (x86_64-redhat-linux)
        compiled by GNU C version 4.1.2 20080704 (Red Hat 4.1.2-48).
GGC heuristics: --param ggc-min-expand=100 --param ggc-min-heapsize=131072
Compiler executable checksum: ad35c03ce9997656f54e642ebd49f167

test.cxx:13: error: statement-expressions are allowed only inside functions
test.cxx:13: error: register name not specified for â__vâ
test.cxx:13: error: expected `)' before â:â token

----------klap-----------------

Don't initialise a const variable at file scope using the return value of a function call - you need to initialise it with a value that can be computed at compile time (which htonl(0x00FFFFFF) cannot).

The (first) error message is actually telling you that.

It's got nothing to do with compiler optimisation settings.

It's not a bug!
The return value of a function is not a constant expression, thus you cannot initialize const variables with function return values! If you make it non-const, it works as expected, however, because it's perfectly legal.