Assign struct member value to struct member value

I'm having a little trouble understanding how to do this properly. It seems like it's something simple that I have just glossed over.

Here are the struct definitions in my header...

Code:

struct source {
	int num;
	int *av[128];
	char *tcpip[128];
	int *tcpport[128];
	char *label[256];
	int *active[128];
	char *sdip[128];
	char *hdip[128];
	char *aip[128];
}source;

struct display {
	int num;
	char *tcpip[128];
	int *tcpport[128];
	int *src[128];
}display;

Here is the line in which I'm trying to assign values where mon_selected is a simple int used to index a selected monitor.

Code:

drag_label(video_bg, source.label[display.src[mon_selected]], samp.x, samp.y, oldx, oldy);

...aaaand the error that I can't seem to get rid of without assigning display.src[mon_selected] to a temporary variable. ick.

Code:

src/touchscreen.c:57: error: array subscript is not an integer

It looks to me like I am not dereferencing the display.src member properly. My guess is that it is not following the pointer to the actual value. I'm not sure how to fix it though.

Enlighten me! Please and thank you.

When these kinds of problems happen, I like to write small programs to try and figure out why the issue is happening. For instance:

Code:

#include <stdio.h>
#include <string.h>

struct display{
        int *src[10];
}display;

int main(void) {
        int i = 0;
        int test = 5;

        for(i=0; i<10; i++){
                display.src[i] = malloc(sizeof(int));
                *display.src[i] = i;
                printf("%d\n", *display.src[i]);
        }

        *display.src[test] = 15;

        printf("\n");

        for(i=0; i<10; i++)
                printf("%d\n", *display.src[i]);

        return 0;
}

When I originally wrote this, I removed the astrix on the red line to see if I could reproduce your compiler error. When I did this, I received the same error. I then compiled the program with the astrix and everything worked properly.

P.S. I'm not checking the return value of malloc or free'ing my malloced memory at the end of the program for simplicity sake. You should always do these things as they are good practice.

Adding the astrix actually makes it compile, but not function. Signal 11 from the kernel.

Well, if your not sure why the astrix fixed it, then I haven't helped you.

What was the index of source.label[] looking for? And what were you giving it?
What did the astrix do when you used it with display.src[mon_selected]?

EDIT: I just saw your reply.....if your getting a segfault, it sounds to me like you haven't set aside any memory for the data. You can reference my previous example to see what I mean.

Alright... what have we learned here.

1) malloc your memory...
2) dereference your pointers when assigning values

Changes in red.

Code:

for(i = 0; i < display.num; i++) {
    display.src[i] = malloc(sizeof(int));
    *display.src[i] = -1;
}

Code:

if((!ret) && (dragging == 1) && (check(samp.x, samp.y) == 3)) {
    if(src_selected > -1) {
        *display.src[0] = src_selected;
        activate_display(0, src_selected);
        clean_loop();
        return 0;
    }
...

Code:

drag_label(video_bg, source.label[*display.src[mon_selected]], samp.x, samp.y, oldx, oldy);

All works as expected now. Thanks for dose of enlightenment.

Glad I could help!

Again, I would recommend checking the return value of malloc() to make sure you don't run out of memory and also remember to free your malloc'ed memory when your done using it.