Scope Example

This simple program shows how the C language handles scope.

/*
 * this is a do-nothing program that demonstrates the
 * scope rules of C.
 */
#include <stdio.h>
#include <stdlib.h>
 
/*
 * forward declarations
 */
void g(int);
void h(void);
 
/* the top-level definition */
int variable = 1;
 
/*
 * the main routine
 */
int main(void)
{
	/* scope is function main */
	int variable = 2;
 
	printf("main(%d):variable = %d\n", __LINE__, variable);
 
	/* now an inner block */
	{
		/* scope is the rest of this block */
		int variable = 3;
 
		printf("main(%d):variable = %d\n", __LINE__, variable);
 		/* now an even more inner block */
		{
			/* scope is this block */
			extern int variable;
 
			printf("main(%d):variable = %d\n", __LINE__,
					variable);
		}
		/* end innermost block */
 
		printf("main(%d):variable = %d\n", __LINE__, variable);
	}
	/* end inner block -- back to main block */
 
	printf("main(%d):variable = %d\n", __LINE__, variable);
 
	/* now let's show how functions interact with scope */
	g(variable);
 
	/* bye! */
	return(EXIT_SUCCESS);
}
 
/*
 * now notice "variable" is a parameter
 * so it (effectively) overrides references to the
 * top-level variable)
 */
void g(int variable)
{
	printf("g(%d):variable = %d\n", __LINE__, variable);
	/* now let's call another function */
	h();
}
 
/*
 * this function has no declarations, so
 * let's see what it prints
 */
void h(void)
{
	printf("h(%d):variable = %d\n", __LINE__, variable);
}