Thread: Pointer Passing Question

Hey great question, this was a personal beef of mine. Don't return a pointer!

Code:

#include<stdio.h>

void testfunc (char *string) {
	int i;
	printf("in testfunc(): %s\n", string);
	for (i=0; i<11; i+=2) string[i]='X';
}	


int main () {	    // 12345678901234567890		
	char string[]="hello world";
	testfunc(string);
	printf("in main(): %s\n", string);
	return 0;
}

Now you can use the return value for something else.

What you have will work, except that you are not allocating memory for path in the first place.

If you actually want to change path by pointing it at a different location, you need the address of the pointer (aka a pointer to pointer), and assign *path = ...;

--
Mats

Code:

int main()
{
    char path[100];
    func(path);
}


void func(char* path)
{
    const char foo[] = "/index.html";
    strncpy(path, foo, sizeof(foo));
}

Or

Code:

int main()
{
    const char* path;
    func(&path);
}


void func(const char** path)
{
    *path = "/index.html";
}

And remember that functions always must have a return type!
If your function will return nothing, you must add "void".

Pointers work on a very simple principle.
All variables are stored in memory, thus have a memory address.
Each time a variable is passed to a function, a new variable of the same type is created and the value is copied over.
So the new local copy will always be modified instead of the original.
So if you pass in the address of the original variable, then the function could just write to that memory address to change the original.
A memory address is stored by a pointer to that type. So if the original variable is char, then a pointer to that becomes char*.
To take the address of a variable, use the & operator. Exceptions are arrays which are automatically converted to pointers when passed.

You know the saddest part is I thought about this when I wrote my last post but decided not to bother adding

Code:

char *string=malloc(12);
strcpy(string,"hello world");

will work in place of

Code:

char string[]="hello world";

but you must remember malloc puts your variable on the heap and so you are responsible for free()ing it...