Re: extern const int n; considered undefined reference?
Jim Michaels wrote 2013-12-28 11:13:
Fri 12/27/2013 20:12:09.39|d:\prj\lib\prsinum\test|>g++ -Wextra -Wall -o
m.exe i.cpp m.cpp
C:\Users\JIM-MI~1\AppData\Local\Temp\ccQU9nKz.o:m.cpp:(.text+0x17):
undefined reference to `n'
collect2.exe: error: ld returned 1 exit status
Fri 12/27/2013 20:12:44.26|d:\prj\lib\prsinum\test|>type i.cpp
const int n=5;
Fri 12/27/2013 20:16:06.97|d:\prj\lib\prsinum\test|>type i.h
extern const int n;
Fri 12/27/2013 20:16:11.93|d:\prj\lib\prsinum\test|>type m.cpp
#include "i.h"
#include <iostream>
int main(void) {
std::cout<<n;
return 0;
}
Fri 12/27/2013 20:16:17.21|d:\prj\lib\prsinum\test|>
why can regular variables be extern'd but not const versions of same?
I would like to import them in a header somehow. but my practices seem
to be failing for an unknown reason.
bad practice? gcc bug? please let me know. I don't have the BNF for
c++11 handy to look at to check against.
A constant defaults to static unless declared otherwise. That makes the
'n' in "i.cpp" invisible outside its module.
The easiest way to fix this is to just include "i.h" in "i.cpp", a good
idea anyway as it lets the compiler verify the declarations in the
header against the definitions in the source file.
Bo Persson
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