C - "warning: format "%c" expects argument of type "char *", but argument 3 has type "int":?

Question

I am writing code to read a PPM file into a struct pixel_type array containing 3 unsigned chars r,g, and b. The code that causes problems looks like this:

struct pixel_type pArray[width][height], *pPtr[width][height];
pPtr[width][height] = &pArray[width][height];

for(h = 0; h < height; h++)
{
    for(w = 0; w < width; w++)
    {
        fscanf(in, "%c%c%c", pPtr[w][h]->r, pPtr[w][h]->g, pPtr[w][h]->b);
    }
}

When compiling, I get this message for all 3 "%c"s:

warning:

format â%câ expects argument of type âchar *â, but argument (3,4, or 5) has type âintâ [-Wformat]

What would be the best way to read the pixel values into the struct pixel_type array?

struct pixel_type
{
    unsigned char r;
    unsigned char g;
    unsigned char b;
};

@Kaz I can add more of my code if you want. I'm not asking for anyone to code for me, I just need to know the best way to take each pixel value (I believe P6 PPM pixel values are stored in binary) and convert them to three chars (r, g, b). Then I can use this info to write a different PPM file. — user2993631, Nov 14 '13 at 20:08
@HighCore You're right, sorry. I kinda want to change it now. Next time. — user2993631, Nov 14 '13 at 20:19
@user2993631 ???? That comment was supposed to be for a completely different question by someone else, and does not apply here. How did that happen ... I'm pretty sure I was on the right question when I typed it. Sorry about that! — Kaz, Nov 14 '13 at 20:21

score 1 · Accepted Answer · answered Nov 14 '13 at 20:08

1

You only need one temporary pointer, not a whole array of them.

struct pixel_type {
    unsigned char r;
    unsigned char g;
    unsigned char b;
    };

main()
{   
    struct pixel_type pArray[10][10], *pPtr;
    int height = 10, width = 10, h, w;
    char buf[32];

    /* testing */

    strcpy(buf, "abc");

    for(h = 0; h < height; h++) {
        for (w = 0; w < width; w++) {
            pPtr = &pArray[width][height];
            /* testing */
            sscanf(buf, "%c%c%c", &pPtr->r, &pPtr->g, &pPtr->b);
            /* fscanf(in, "%c%c%c", &pPtr->r, &pPtr->g, &pPtr->b); */
        }
    }
}

answered Nov 14 '13 at 20:08

Arun Taylor

1,574
8
5

Thanks, I think that fixes it. My rep's too low to "vote up", but I appreciate it. – user2993631 Nov 14 '13 at 20:17
You don't need any temporary pointer at all. Just use `&pArray[width][height].r`, etc. – R.. GitHub STOP HELPING ICE Nov 14 '13 at 22:48

fvdalcin · Answer 2 · 2013-11-14T20:15:31.850

You don't need to declare a pointer to the array *pPtr[width][height], since pArray[width][height] is already an array and this:

pArray[0][0];

is equivalent to this:

*pArray;

In the same way that this:

&pArray[0][0];

Is equivalent to this:

pArray;

So you just need to point the address of where your data is (inside of the structure), after the pointer or the array had already been deferenced.

struct pixel_type pArray[width][height];

for(h = 0; h < height; h++)
{
    for(w = 0; w < width; w++)
    {
        fscanf(in, "%c%c%c", &(pArray[w][h].r), &(pArray[w][h].g), &(pArray[w][h].b));
    }
}

score 0 · Answer 3 · answered Nov 14 '13 at 20:12

0

Changing your 2D array of pointers pPtr[width][height] to a pointer pPtr will solve your problem.

answered Nov 14 '13 at 20:12

haccks

104,019
25
176
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C - "warning: format "%c" expects argument of type "char *", but argument 3 has type "int":?

3 Answers3