C/C++ : exporting variable from a .h -

in c/c++, use main.cpp ready-to-use variable (mtab) :

1. declared , initialized in lib.h
2. implemented in lib.cpp

i can't make work : what's wrong ? seems typedef ignored , don't why ?

note :

1. as mtab must same each user of lib.h, added static keyword
2. as static variable must initialized (to avoid unexpected behavior), initialized mtab in lib.h
3. when move mtab initialisation in lib.cpp : compilation ko
4. when move mtab declaration , initialisation in lib.cpp, and, use "extern" in main.cpp : compilation ko
5. the way compilation ok put mtab declaration , initialisation inside main scope in main.cpp... not want ! (inside main scope compilation ok. outside main scope, @ include level, compilation ko)

thanks help,

fh

~>more * 

lib.cpp

#include "lib.h"  void m1 ( unsigned int const idatasize, int * const iopdata ) { return; } void m2 ( unsigned int const idatasize, int * const iopdata ) { return; } 

lib.h

#ifndef __lib__ #define __lib__ void m1 ( unsigned int const idatasize, int * const iopdata ); void m2 ( unsigned int const idatasize, int * const iopdata ); typedef void ( *pf ) ( unsigned int const idatasize, int * const iopdata ); static pf mtab[2]; // ready-to-use variable exported mtab[0] = &m1; mtab[1] = &m2; #endif 

main.cpp

#include "lib.h" #include <stddef.h> // null  int main () {   (*mtab[0]) ( 0, null );   (*mtab[1]) ( 0, null );    return 0; } 

makefile

all:     gcc -i. -c lib.cpp -o lib.o     gcc -i. -c main.cpp -o main.o     gcc -i. lib.o main.o -o main.exe 

console:

~>make gcc -i. -c lib.cpp -o lib.o in file included lib.cpp:1:0: lib.h:7:1: error: ‘mtab’ not name type lib.h:8:1: error: ‘mtab’ not name type make: *** [all] error 1 

first, put declarations, not definitions of objects or functions, in shared header files. mtab, use in lib.h:

extern pf mtab[2]; 

second, define object in 1 , 1 source file. put in lib.cpp:

pf mtab[2] = { m1, m2 }; 

third, mtab[0] = &m1; not initialization of mtab. assignment statement, in wrong place, because cannot have assignment statements @ file scope. proper way initialize mtab shown above. (assignments different initializations. assignments executable statements , must inside function bodies. initialization part of creation of object, may happen prior primary execution of program.)

fourth, static not make object same each user. has 2 effects, may vary depending on used. when used @ file scope, says identifier has internal linkage, means identifier refers only object in current compilation; not linked externally same identifier in other compilations. means opposite of wrote; means each source file has own mtab, not share 1 mtab. (the second effect of static static give object static storage duration, lifetime entire execution of program. however, has no effect @ file scope because object declared @ file scope has static storage duration default.)