Beginner question about pointers

This is a discussion on Beginner question about pointers within the C Programming forums, part of the General Programming Boards category; Code: void function(char * ptrA, char arr1[]) { ... ptrA = arr1[9]; ... } Code: int main(...) { ... char ...

  1. #1
    Registered User
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    Beginner question about pointers

    Code:
    void function(char * ptrA, char arr1[])
    {
    	...
            ptrA = arr1[9];
            ...
    }
    Code:
    int main(...)
    {
            ...
            char arr1[10];
            fillArray(arr1); // fills the array
            char *ptrA = arr1[1];
            function(ptrA, arr1);
    ...
    }
    After the call to function(), does ptrA point to arr1[1], or arr1[9]? If it points to arr1[1], what do I need to do so that I can make persistent changes on ptrA inside of the scope of function()? Thanks in advance.

  2. #2
    and the Hat of Guessing tabstop's Avatar
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    Nov 2007
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    14,185
    A function cannot change the value passed into it. ptrA was passed into a function, whatever happens inside that function stays in Vegas, and it has the same value (in main) afterwards.

  3. #3
    Guest Sebastiani's Avatar
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    First of, let's just clarify that array indexes start at 0 (you may already know that, but I'm just making sure). Second, arr1[N] is a char. To get the address of a char (or any variable, for that matter), use the 'address-of' operator ('&'). Finally, all parameters are passed by value in C, so to 'repoint' a pointer, you need to pass it's address (in this case, a char**).

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