My program consists of several files. Suppose some data and functions in file a must also be accessed by file b. I want to extern these in a header file a.h and #include that in file a and b. This is OK for functions as the extern becomes the prototype when a.h is included in a.c, but with variables you can't have an external reference to a variable in the same file that defines it. What should I do?
Who says?you can't have an external reference to a variable in the same file that defines it.
Code:itsme@itsme:~/C$ cat extern1.c #include <stdio.h> #include "myextern.h" int main(void) { printf("a in main is %d\n", a); foo(); return 0; }Code:itsme@itsme:~/C$ cat extern2.c #include <stdio.h> #include "myextern.h" int a = 5; void foo(void) { printf("%d\n", a); }itsme@itsme:~/C$ gcc -Wall extern1.c extern2.c -o externCode:itsme@itsme:~/C$ cat myextern.h extern void foo(void); extern int a;
itsme@itsme:~/C$ ./extern
a in main is 5
5
If you understand what you're doing, you're not learning anything.
This is just what I wanted to do but my compiler compained that the variable was already declared. Perhaps I was doing something else wrong, I'll go back and look again.
Many thanks for your help.
Sounds like you forgot to use the "extern" keyword:
In .h:
extern int a;
When all else fails, read the instructions.
If you're posting code, use code tags: [code] /* insert code here */ [/code]
