question about pointers

[blob84]

Hi, why if i call writelines all woks, but if i call *lineptr++ inside the main, it doesn't and i get "error: lvalue...:

#include <stdio.h>
	
#define MAXLINES 1000

void writelines(char *lineptr[], int nlines);

int main(void)
{
	char *lineptr[MAXLINES];

	int nlines;
	for( nlines = 0; nlines < 5; nlines++)
		lineptr[nlines] = "ciao\n";
	
	//writelines(lineptr, nlines);

        while (nlines-- > 0)
		printf("%s\n", *lineptr++);
}

void writelines(char *lineptr[], int nlines)
{
	while (nlines-- > 0)
		printf("%s\n", *lineptr++);
}

[Adak]

In main(), lineptr is the name of an array - yes, it has the address of the base element, but it's an array, and has a sizeof() that reflects it. (try it).

In any other function, the array is sent as a pointer, and it's sizeof() becomes just the size of the pointer itself. You can always increment a pointer, but you can't increment the name of an array, before it has been "degraded" to a pointer.

[blob84]

ok to let it work it should be assigned to a pointer of pointers, so in a function as Adak says *lineptr[ ] is **lineptr:

#include <stdio.h>
	
#define MAXLINES 1000

void writelines(char *lineptr[], int nlines);

int main(void)
{
	char *lineptr[MAXLINES];
	char **h = lineptr;

	int nlines;
	for( nlines = 0; nlines < 5; nlines++)
		lineptr[nlines] = "ciao\n";
	
	while (nlines-- > 0)
		printf("%s\n", *h++);
}