Pointer Stew

[Bharat Lal Madhyani]

Please ignore my previous posting. This is the most recent posting. There were
some type-errors in the previous one. Sorry :-)

/*************/
/* program1.c*/
/*************/

/*
   consider the following small c_program
   path :  is an array of pointers to characters, 
	   which has been initialized
p_path :   is a pointer to path, i.e it is a 
	   pointer to pointer to character

The program basically travels the array path and prints the character string
associated with the pointer at that time.

*/
char *path[]  = {

		"/usr/pgmr/blm/citoh/shit",     
		"/usr/pgmr/junk",   	
		"/usr/lib/news/history",
		"/usr/bin/vi",
		"Testing Initialization",
		0
};

char **p_path = path ; /* pointer to path */
main()
{
	while ( **p_path ) 
		printf("%s\n", *p_path++ );
}


/***************/
/* program2.c  */
/***************/
/* 
     In this program , I have defined a new variable
     bad_address -- which is a pointer to character. And
     while initializing the path array of pointers to characters
     I am getting the following error :

	"program2.c", line 30: illegal initialization


	why it is so ? bad_address is also an address(pointer), which also
	points to character string. And as we all know that two
	dimensional array are implemented through pointers, i.e
	char a[10][20] means :

		a is an array of 10 pointers, and each element of
		array a is an array of  20 characters.

*/
	
char *bad_address = "Testing Initialization";
char *path[]  = {

		"/usr/pgmr/blm/citoh/shit",     
		"/usr/pgmr/junk",   	
		"/usr/lib/news/history",
		"/usr/bin/vi",
		bad_address,           /* Here is illegal initialization */
		0
};
char **p_path = path ; /* pointer to path */
main()
{
	while ( **p_path ) 
		printf("%s\n", *p_path++ );
}


/***************/
/* program3.c  */
/***************/
/* 
     Still consider another program, where I have defined 5 different
     character arrays, and I am Initializing the *path[] with these
     arrays, and the program works fine.

*/
char a1[]="/usr/pgmr/blm/citoh/shit";     
char a2[]="/usr/pgmr/junk";   	
char a3[]="/usr/lib/news/history";
char a4[]="/usr/bin/vi";
char bad_address[] = "Testing Initialization";
char null[]="" ;
char *path[6] = {
		a1,
		a2,
		a3,
		a4,
		bad_address,
		null
		};

char **p_path = path ; /* pointer to path */
main()
{
	while ( **p_path ) 
		printf("%s\n", *p_path++ );
}

/***************/
/* program4.c  */
/***************/
/* 
     Still consider another program, where I have defined 5 different
     character pointers, and I am Initializing the *path[] with these
     pointers, and the program does not compile due to illegal 
     initialization.

*/
char *a1="/usr/pgmr/blm/citoh/shit";     
char *a2="/usr/pgmr/junk";   	
char *a3="/usr/lib/news/history";
char *a4="/usr/bin/vi";
char *bad_address = "Testing Initialization";
char *null="" ;
char *path[6] = {
		a1,
		a2,
		a3,
		a4,
		bad_address,
		null
		};

char **p_path = path ; /* pointer to path */
main()
{
	while ( **p_path ) 
		printf("%s\n", *p_path++ );
}
/* I am getting the following errors:

"program3.c", line 19: illegal initialization
"program3.c", line 20: illegal initialization
"program3.c", line 21: illegal initialization
"program3.c", line 22: illegal initialization
"program3.c", line 23: illegal initialization
"program3.c", line 24: illegal initialization

*/


Questions :

.	What subtle difference program3.c & program4.c has ?

.	Why character arrays can be used to initialize the array
	of pointers to character & character pointers cannot be
	used to initialize the array of pointers to characters ?


--
spec0!blm
Bharat Madhyani