Thread: Passing pointers into function

I want to scan numbers in from within a function, but have access to them in main, so I tried using pointers to do so:

Code:

// Path Of Exile socket colours simulation

#include <stdio.h>
#include <stdlib.h>
#include <time.h>

#define TRUE 0==0
#define FALSE 0==1
#define RED 0
#define GREEN 1
#define BLUE 2
#define ALL 3

int isNum(char *s);
int scanSockets(int *colourP[ALL], int sockets);

int main(int argc, char **argv) {
    if (argc != 2 || isNum(argv[1]) == FALSE) {
        fprintf(stderr, "Format: ./poeChrom <num simulations>\n");
        return 1;
    }

    int sockets;
    int colour[ALL] = {0};
    int *colourP[ALL] = {&colour[RED], &colour[GREEN], &colour[BLUE]};
    int flag = FALSE;
    
    printf("\n\tNumber of linked sockets: ");
    scanf("%d", &sockets);
    printf("\t-----\n\tSockets that are wished for\n"
           "\t(format \"<R num> <G num> <B num>\" in that order)\n"
           "\te.g. 1 2 2 for 1R 2G 2B: ");
           
    if (scanSockets(colourP[ALL], sockets) == FALSE) {
        fprintf(stderr, "Invalid entry\n\n");
        return EXIT_FAILURE;
    } else
        printf("SUCCESS\n");

    return EXIT_SUCCESS;;
}

int isNum(char *s) {
    
    for (; *s != '\0'; s++)
        if (*s < '0' || *s > '9') return FALSE;

    return TRUE;
}

int scanSockets(int *colourP[ALL], int sockets) {
    int colour[ALL];
    int i, scan, valid = TRUE;
    int sum = 0;
    
    scan = scanf("%d %d %d", colour[RED], colour[GREEN], colour[BLUE]);
    if (scan != 3)
        return FALSE;
        
    for (i=0; i<ALL; i++) {
        if (colour[i] < 0) valid = FALSE;
        sum += colour[i];
    }
    if (sum == 0 || sum > sockets) valid = FALSE;
    
    for (i=0; i<ALL; i++) *colourP[i] = colour[i];
    //printf("IN FUNC = %d %d %d\n", colour[RED], colour[GREEN]
    //                                        , colour[BLUE]);
    
    return valid;
}

But I'm getting the errors

poeChrom.c: In function ‘main’:
poeChrom.c:34:5: warning: passing argument 1 of ‘scanSockets’ from incompatible pointer type [enabled by default]
poeChrom.c:15:5: note: expected ‘int **’ but argument is of type ‘int *’
poeChrom.c: In function ‘scanSockets’:
poeChrom.c:56:5: warning: format ‘%d’ expects argument of type ‘int *’, but argument 2 has type ‘int’ [-Wformat]
poeChrom.c:56:5: warning: format ‘%d’ expects argument of type ‘int *’, but argument 3 has type ‘int’ [-Wformat]
poeChrom.c:56:5: warning: format ‘%d’ expects argument of type ‘int *’, but argument 4 has type ‘int’ [-Wformat]

If you can't follow what I'm trying to do, just ask and I'll try my best to explain it. Thanks!

Originally Posted by oogabooga

If I understand your intent you don't need colourP at all. Just pass colour to your function and don't declare another colour in it. And you need ampersands in front of colour[RED], etc., in your scanf.

ALL would be better named NUM_COLOURS.

You'll want to put parens around 0==0 and 0==1 in your defines (or simply use 1 and 0). A nicer way to do this is

Code:

enum BOOL {FALSE, TRUE};

You, also, don't want #define FALSE (0==0) at all, because that expression is, well, true

Originally Posted by oogabooga

If I understand your intent you don't need colourP at all. Just pass colour to your function and don't declare another colour in it.

That won't do because I'm going to be using the numbers I scanned in not only in the function, but later on outside of the function too.

Originally Posted by oogabooga

And you need ampersands in front of colour[RED], etc., in your scanf.

Yes, thanks for spotting that.

Originally Posted by oogabooga

ALL would be better named NUM_COLOURS.

I'll be using it a lot and would rather stick to the shorter word, but I'll keep that in mind.

Originally Posted by oogabooga

You'll want to put parens around 0==0 and 0==1 in your defines (or simply use 1 and 0). A nicer way to do this is

Code:

enum BOOL {FALSE, TRUE};

Are the parenthesis necessary? And how do I use that enum line exactly?

Originally Posted by c99tutorial

It looks like the following call is wrong:

Code:

scanSockets(colourP[ALL], sockets)

colourP[ALL] is a single member of the array when you probably want to pass the array itself to the function

Code:

scanSockets(colourP, sockets)

Yes thank you! That's exactly what I needed. It all works as intended now

Thanks Hodor, that makes a lot of sense now.

Originally Posted by laserlight

If you don't want to (or cannot, because you are compiling with respect to pre-C99) use what is provided by <stdbool.h>, and if you don't want to use the enum solution, then you might as well go with:

Code:

#define TRUE 1
#define FALSE 0

since (0 == 0) will definitely evaluate to 1 and (0 == 1) will definitely evaluate to 0.

If I use

Code:

enum BOOL {FALSE, TRUE}

then I'm guessing FALSE is replaced with 0 and TRUE with 1, right? But do I also need to add this enum line in all of the functions that I want to use it in? The benefit of the define is that I just need to write it once before my main function.

I used to use 0 and 1, but then our new professor seemed to prefer equalities and it just caught on. I'm not sure why he prefers it now that I think about it.