C program malloc with array of strings

Question

At the beginning of a program I need to dynamically allocate memory for an unknown number of strings with unknown number of size to later manipulate with. To get the number of strings from a user I have:

int main(int argc, char *argv[]){

int number = atoi(argv[1]);

So far so good. "number" now holds holds the number that the user inputted on the command line for executing the code. Now here comes the part I don't quite understand. I now need to dynamically store the lengths of the strings as well as the contents of the strings. For example, I want the program to function like this:

Enter the length of string 1: 5
Please enter string 1: hello
Enter the length of string 2: ...

For this I recognize that I will have to create an array of strings. However, I can't quite understand the concept of pointers to pointers and what not. What I would like is perhaps a simplification of how this gets accomplished?

Answer 1

You know from the start you will have number strings to store so you will need an array of size number to store a pointer to each string.

You can use malloc to dynamically allocate enough memory for number char pointers:

char** strings = malloc(number * sizeof(char*));

Now you can loop number times and allocate each string dynamically:

for (int i = 0; i < number; i++) {
   // Get length of string
   printf("Enter the length of string %d: ", i);
   int length = 0;
   scanf("%d", &length);

   // Clear stdin for next input
   int c = getchar(); while (c != '\n' && c != EOF) c = getchar();

   // Allocate "length" characters and read in string
   printf("Please enter string %d: ", i);
   strings[i] = malloc(length * sizeof(char));
   fgets(strings[i], length, stdin);
}