Getting value from a pointer parameter of a function in C

Question

as I am starting to study at university we are learning how to write in C and we got to the point where I've learned that I can use pointers as function parameters but what they haven't told us is how to get the value from it. I am not able as a person who doesn't know about C as much, to come up with other solution than use two parameters (one as pointer to the variable and other as value. See the example which is not real code but it's just for purpose of demonstration:


int main(int argc, char* argv []) {

     int a;
     addNumber(&a);


}

void addNumber(int * a) {
     *a = *a + 1; // this obviously does not work
}

Any input would be appreciated. Thanks!

Mysticial · Accepted Answer · 2011-10-21 14:20:03Z

3

Only one major thing: You forgot to initialize a. Otherwise, it looks fine.

 int a = 0;
 addNumber(&a);

The only other thing is that you're missing the return statement in main.

edited Oct 21, 2011 at 14:20

answered Oct 21, 2011 at 14:11

Mysticial

473k46 gold badges343 silver badges337 bronze badges

Sign up to request clarification or add additional context in comments.

3 Comments

Jon Over a year ago

a is not initialized, maybe that's why the OP thinks it doesn't work?

Adrien Plisson Over a year ago

and a is missing an initialization value.

Jonathan Leffler Over a year ago

And C99, regrettably, sanctions omitting that return - to follow C++98 which also sanctions the omission of the return from main(). The effect is as if you wrote return 0;.

ObscureRobot · Accepted Answer · 2011-10-21 14:14:53Z

0

Here is an example that may be closer to what you are looking for:

#include <stdio.h>

void increment(int *a, int *b)
{
    *a = *a + *b;
}

int main(void)
{
    int sum = 5;
    int increment_by = 7;
    printf("sum: %d, increment_by: %d\n", sum, increment_by);
    increment(&sum, &increment_by);
    printf("sum: %d, increment_by: %d\n", sum, increment_by);

    return 0;
}

output:

$ ./bar
sum: 5, increment_by: 7
sum: 12, increment_by: 7

answered Oct 21, 2011 at 14:14

ObscureRobot

7,3342 gold badges30 silver badges36 bronze badges

3 Comments

Martin Over a year ago

Thanks I didn't realize it would make such a difference.

ObscureRobot Over a year ago

So others can learn - what part of my answer made a difference for you?

Martin Over a year ago

The inicialization, From you example and by comparing it to my code I immediately realized that I forgot to inicialize the variables and I didn't realize it would cause the problem. Rookie mistake. :-)

Ed Heal · Accepted Answer · 2011-10-21 14:15:29Z

0

It will work. It will work better if you initialise a, to some value.

answered Oct 21, 2011 at 14:15

Ed Heal

60.3k18 gold badges91 silver badges137 bronze badges

Collectives™ on Stack Overflow

Getting value from a pointer parameter of a function in C

3 Answers 3

3 Comments

3 Comments

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

3 Answers 3

3 Comments

3 Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Related