CITS2002 Systems Programming  
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Passing pointers to functions

Consider a very simple function, whose role is to swap two integer values: 

#include <stdio.h>

void swap(int i, int j)
{
    int temp;

    temp = i;
    i    = j;
    j    = temp;
}

int main(int argc, char *argv[])
{
    int a=3, b=5;  // MULTIPLE DEFINITIONS AND INITIALIZATIONS  

    printf("before a=%i, b=%i\n", a, b);

    swap(a, b);    // ATTEMPT TO SWAP THE 2 INTEGERS

    printf("after  a=%i, b=%i\n", a, b);
    return 0;
}

before a=3, b=5
after  a=3, b=5

Doh! What went wrong?

The "problem" occurs because we are not actually swapping the values contained in our variables a and b, but are (successfully) swapping copies of those values.

 

CITS2002 Systems Programming, Lecture 12, p1, 29th August 2023.