char and extern uses

[-EquinoX-]

Say that I have defined :


char tokenString[MAXTOKENLEN+1];

in a file called test.h

and I want to use the value tokenString[MAXTOKENLEN+1];

in another file also, so far I tried:

extern char* tokenString;

but whenever I tried to run the code it always gives me a segmentation fault, can you guys help me out what's wrong here

[tabstop]

Variables in .h files = very very very very very very very bad.
Put extern char tokenString[MAXTOKENLEN+1] in the header file, and include it where you need to see the variable.
ONE .c file has char tokenString[MAXTOKENLEN+1] declared (without the extern).

[-EquinoX-]

Variables in .h files = very very very very very very very bad.
Put extern char tokenString[MAXTOKENLEN+1] in the header file, and include it where you need to see the variable.
ONE .c file has char tokenString[MAXTOKENLEN+1] declared (without the extern).

sorry my mistake I did not write it in the .h file instead in the .c file, sorry .. can you clarify what you mean?

[tabstop]

You can have "extern char tokenString[MAXTOKENLEN+1]" as many times as you like.

You can only have "char tokenString[MAXTOKENLEN+1]" once, and you must have it once. Note that the definition cannot be inside main(), it has to be at global scope.

[-EquinoX-]

I cannot do extern char tokenString[MAXTOKENLEN+1] as maxtokenlen+1 is only defined once in that file, so does that mean that I need to have #define maxtokenlen+1 all over the place as well??

[zacs7]

So define it in a header and include as required...

constants.h (terrible name )

#ifndef INCLUDED_CONSTANTS_H
#define INCLUDED_CONSTANTS_H

/* probably best to include the +1 here... */
#define MAXTOKENLEN 32

#endif /* INCLUDED_CONSTANTS_H */

header.h

#ifndef INCLUDED_HEADER_H
#define INCLUDED_HEADER_H

#include "constants.h"

extern char tokenString[MAXTOKENLEN];

#endif /* INCLUDED_HEADER_H */

main.c

#include <stdio.h>

#include "constants.h"
#include "header.h"

/* ... */

char tokenString[MAXTOKENLEN];

int main(void)
{
   /* ... */
   return 0;
}

Of course there is nothing stoping you from defining MAXTOKENLEN and extern char tokenString[] in the same header.

[-EquinoX-]

why can't I just define it as extern char* tokenString??

[Elysia]

Because it's not the same type. You're trying to tell the compiler there is an extern variable with a name and different type than there is.

[-EquinoX-]

Isn't a char* abc basically the same as char abc []? sorry to ask such a dumb question.. I haven't programmed in C for a while

[IceDane]

Isn't a char* abc basically the same as char abc []? sorry to ask such a dumb question.. I haven't programmed in C for a while

Yes and no. When you pass a character array to a function, it degenerates to a pointer. Even though char * and char [] is almost the same, it isn't completely, and to the compiler, it's not the same type.

[Elysia]

In prototypes, they are the same:

void foo(int* x);
void foo2(int x[]);

Otherwise, they are not the same.