Thread: Realloc/Pass by reference quagmire

I created a function to read in stations. Input is fine. So what I do is, in main(), pass in the array to the function. Then in the function, realloc the size of the array to the number of stations found reading in the file and then I realloc the number of characters it can hold. The errors I get are:

1) in realloc(): warning: junk pointer, too high to make sense (this is repeated for what looks the number of stations I have)

2) pointer to wrong page

2) Core dumped - seg fault.

Here is my code (not showing stuff that works fine):
In main():

Code:

char **list;

// So want to hold 1 string
list = malloc(1 * sizeof(*list));

// Then want the string to hold 1 char + \0
list[0] = malloc(1*sizeof(char)+1);

read(&*list);

In read():

Code:

// So now realloc to hold "num" strings
*list = realloc(*list, num * sizeof(*list));

// Realloc so that the strings can hold 6 chars now
for(i=0;i<num;++i){
     list[i] = realloc(list[i], 6 * sizeof(char));
}

// Now copy the string input
for(i=0;i<num;++i){
    strcpy(list[i], input[i]);
}

//print out the new info

for(i=0;i<num;++i){
    printf(%s is the new place.\n", list[i]);
}

Any ideas? Interesting is that I can pass a char in, 5, and i can print it inside the function. But after that -- only problems...

None of my functions are the same as syscalls... read() is actully a longer function name...

Any ideas why I cannot realloc?

Originally Posted by towed

None of my functions are the same as syscalls... read() is actully a longer function name...

Any ideas why I cannot realloc?

I updated my last post so re-read it and do note the difference in the realloc() call.

Yep!

Well, it appears I am getting tripped up when allocate the necessary space for every string... Still getting junk pointer, too high to make sense.

Ahh... Interesting... I was thinking of something similar -- just passing **list in and not mallocing space for the number of characters in the string and instead just do it in the function.

Thanks! Did not know that about realloc. Neat idea of reallocing the one then mallocing the others...

Hmm new issue...
Seems it has been accomplished, but how do I reference it outside that function and in main?

I tried printing it to the screen outside the function, just as list[i], in a for loop. But get a seg fault. Similary tried adding a * and an & to no avail.

How about posting the updated code?

I can't really, this part is just a small cog of a large program...

Where I am at it is, I can print inside the read() function, the different id's in the array that I passed in.

Now in main(), when trying to print out the same ids (using the same print statement and for loop combo) it seg faults.

In main():

Code:

for(i=0;i<num;++i){
    printf(%s is the new place.\n", list[i]);
}

I thought I passed the reference in, such that I can use the list outside that function...

Ideas?

Probably you should read Question 4.8

It looks like you're running into a scope issue.
Think about having your realloc function return a pointer so the array pointer is updated outside the fuction.
Alternatively declare your array pointer globally.

Ok, seems to be working. I made struct to hold it, allocate memory for a pointer to the struct... passed it in. And now can use the list outside the function -- is that what you were getting at?