copying array of string pointers to a new array in C - c

Question

we get input from user (command line) and store it in in char* input[].
This input will look like this, when the user inputs all required information:
input[]: add John Smith (male) <relation> Emma Stone (female).
Then we want to copy it to new_input[] with 8 positions (for example John would be on the position 1). In our first example this will look like the same:
new_input []: add John Smith (male) <relation> Emma Stone (female)
But there are possibilities that we don't get all the information from the user. Especially it is most likely we don't get the last name. So, during the copy we need to add some ‘if-statements’ to check if the user puts e.g. Smith or not. If not – we want write ‘NULL’ at the positions 2 and 6. The array looks then like:
if input []: add John (male) <relation> Emma (female)
new_input []: add John NULL (male) <relation> Emma NULL (female)
Unfortunately, we have difficulties with copying array of string pointers to a new array.
We tried memcpy(), new_input[i] = input[i] (in a for-loop).
EDIT: here is code and i also edit example above, (new_input with NULL on position 2 and 6 if last names are missing)
`int main(int argc, char* argv[])
{
char* copy_input = NULL;
int len_max = 256;
int error = 1;
char* input = (char*) malloc(len_max* sizeof(char));
if (argc == 1)
{
while(1)
{
printf("cmd> ");
char read[len_max];
input = fgets(read, len_max, stdin);
int len = strlen(read);`
if(read[len-1] == '\n')
{
read[len-1] = '\0';
}
copy_input = input;``
error = handleUserInput (copy_input);
}`
in handle user command, we split string by space and check first string, if it is " add " , go to function addCommand (in)
`
int handleUserInput(char* input) // takes char input from main and compares type of command
{
printf("input: %s\n",input );
char* in[8];
int i = 0;
char* temp;
char delimiter[] = " ";
temp = strtok(input, delimiter);
in[i++] = temp;
while( temp != NULL)
{
temp = strtok(NULL, delimiter);
in[i++] = temp;
// printf("%s\n", temp);
}
if(!strcmp(in[0], "add"))
{
addCommand(in);
}`
In function add command, we want to do copy input to new_input as i described above...
`int addCommand(char* input[]) //
{
char* new_input[];
`

Answer 1

If you are using the new_input[i] = input[i]
You're gonna assign the pointeur of input[i] to the new_input[i]
then thing is that it would not be a copy it's just a copy of the string personnal adress.
So if u want to make a real copy with it's "own memory" u need to first allocate a new string and then copy the content of the last string in the new.
(man strdup)
To copy an array of string pointer you will probably do a basic method wich mean to first allocate your double pointeur (char **array)
to receive your new content.
and then loop to copy all the content with the method that i've show you just before