Using extern in C doesn't work as expected
I have created two files:
tunables.h
#ifndef TUNABLES_H
#define TUNABLES_H
void tunables_load_conservative();
void tunables_load_aggressive();
extern int timer_x;
#endif /*TUNABLES_H */
and tunables.c
#include "tunables.h"
int timer_x;
void tunables_load_conservative(){
timer_x = 3;
}
void tunables_load_aggressive(){
timer_x = 1;
}
All the other files of my project includes "tunables.h". When I load the project both A.c and B.c calls tunables_load_conservative but if, after a while, I call in file A.c tunables_load_aggressive() in file B.c the timer_x remains 3. Why?
This is my Makefile:
INCLUDE=`pwd`/include
GCCFLAGS= -a开发者_JAVA百科nsi -O3 -pedantic -Wall -Wunused -I${INCLUDE} -DDEBUG
GCCOTHERFLAGS= -ggdb -pg
all: A B
A: A.o tunables.o
gcc -o A ${GCCFLAGS} ${GCCOTHERFLAGS} tunables.o
B: B.o tunables.o
gcc -o LBfixed ${GCCFLAGS} ${GCCOTHERFLAGS} tunables.o
A.o: A.c
gcc -c ${GCCFLAGS} ${GCCOTHERFLAGS} A.c
B.o: B.c
gcc -c ${GCCFLAGS} ${GCCOTHERFLAGS} B.c
tunables.o: tunables.c
gcc -c ${GCCFLAGS} ${GCCOTHERFLAGS} tunables.c
clean:
rm -rf *.o A B
It looks like you've got two separate processes, A and B. The extern
declaration does not set up shared memory across processes, but instead allows different compilation units within the same process to access the same variable.
To share a variable across processes, you will need to use system-dependent IPC methods.
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