Dynamic Array of char Pointer

Question

I am trying to define a dynamic array containing char pointers that point to strings. The string can be of any length, so i used char pointers. I want to dynamically resize the array each time I need to store more values. The following code gives me segmentation fault. Am I doing it well?

int main() {
    char **input=NULL;
    char *buffer;

    int i=0;

    do {
        input = (char **)realloc(input, (i+1) * sizeof(char *));

        scanf("%s", &buffer);
        strcpy(input[i++],buffer);

    } while(strlen(buffer)!=0);


}

cnicutar · Accepted Answer · 2011-11-30 14:38:32Z

8

There are multiple issues in your code. It won't work until you fix all of them

You aren't allocating memory for buffer. Scanf would write into thin air, if it weren't for the next point which is arguably more serious
You should pass buffer to scanf, not &buffer
You aren't allocating memory for input[i]. You are only allocating memory for input.

answered Nov 30, 2011 at 14:38

cnicutar

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Comments

wildplasser · Accepted Answer · 2011-11-30 14:41:12Z

1

buffer is uninitialized. Besides &buffer is a pointer to a pointer, not to a character array, as you probably intend.

answered Nov 30, 2011 at 14:41

wildplasser

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Some programmer dude · Accepted Answer · 2011-11-30 15:00:31Z

1

The problem is that you define buffer as a pointer, but you do not point it to something that can hold the scanned string, so scanf writes out in unallocated memory which is really bad. You also do not allocate input[i] so strcpy will also fail. You might want to change that to use strdup instead:

input[i++] = strdup(buffer);

Another couple of nitpicks: When scanning for a string, you do not need the & on the string buffer, so redo like this:

scanf("%s", buffer);

And you should not cast the result of realloc (or malloc either for that matter):

input = realloc(input, (i+1) * sizeof(char *));

answered Nov 30, 2011 at 15:00

Some programmer dude

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hmjd · Accepted Answer · 2011-11-30 15:05:50Z

1

In addition to the issues already listed in the other answers the loop will never terminate as:

scanf("%s", buffer);

will not return until it reads at least one character, excluding the end of line character.

answered Nov 30, 2011 at 15:05

hmjd

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ziu · Accepted Answer · 2011-11-30 14:39:56Z

0

Your buffer and your input[i] are not allocated.

answered Nov 30, 2011 at 14:39

ziu

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