Page 142 - C-Language

int main(void)
{
g_myglobal = 42;
return 0;
}

See also How do I use extern to share variables between source files?

Using Global Constants

Headers may be used to declare globally used read-only resources, like string tables for example.

Declare those in a separate header which gets included by any file ("Translation Unit") which
wants to make use of them. It's handy to use the same header to declare a related enumeration to
identify all string-resources:

resources.h:

#ifndef RESOURCES_H
#define RESOURCES_H

typedef enum { /* Define a type describing the possible valid resource IDs. */
RESOURCE_UNDEFINED = -1, /* To be used to initialise any EnumResourceID typed variable to be

marked as "not in use", "not in list", "undefined", wtf.
Will say un-initialised on application level, not on language
level. Initialised uninitialised, so to say ;-)
Its like NULL for pointers ;-)*/
RESOURCE_UNKNOWN = 0, /* To be used if the application uses some resource ID,
for which we do not have a table entry defined, a fall back in
case we _need_ to display something, but do not find anything
appropriate. */

/* The following identify the resources we have defined: */
RESOURCE_OK,
RESOURCE_CANCEL,
RESOURCE_ABORT,
/* Insert more here. */

RESOURCE_MAX /* The maximum number of resources defined. */
} EnumResourceID;

extern const char * const resources[RESOURCE_MAX]; /* Declare, promise to anybody who includes

this, that at linkage-time this symbol will be around.
The 1st const guarantees the strings will not change,
the 2nd const guarantees the string-table entries
will never suddenly point somewhere else as set during
initialisation. */
#endif

To actually define the resources created a related .c-file, that is another translation unit holding the
actual instances of the what had been declared in the related header (.h) file:

resources.c:

https://riptutorial.com/ 118