Question

There’s no way to know how many arguments there are; the user can provide a list of indeterminate length.

I’m very bad with C. How can I read arguments out of the command-line array and into a new array of strings?

Frankly I don’t even know how to make an array of separate strings, if I’m going to be honest. An example would be super-helpful.

Answer 1

Yes there is.

If you look at the main function’s full prototype:

int main(int argc, char **argv, char **env)

argc: This is the argument counter, it contains the number of argument given by the user (Assumin the command is cd, entering cd home will give argc = 2 because the command name is always argument 0)

argv: This is the arguments values, it is an array of size argc of char* pointing to the arguments themselves.

env: This is a table (as argv) containing the environment when the program is called (through a shell for example, it’s given with env command).

As for an example of making an array of things: Two ways are possible:

First, a fixed-length array:

char tab[4]; // declares a variable "tab" which is an array of 4 chars
tab[0] = 'a'; // Sets the first char of tab to be the letter 'a'

Second, a variable-length array:

//You cannot do:
//int x = 4;
//char tab[x];
//Because the compiler cannot create arrays with variable sizes this way
//(If you want more info on this, look for heap and stack memory allocations
//You have to do:
int x = 4; //4 for example
char *tab;
tab = malloc(sizeof(*tab) * x); //or malloc(sizeof(char) * x); but I prefer *tab for
//many reasons, mainly because if you ever change the declaration from "char *tab"
//to "anything *tab", you won't have to peer through your code to change every malloc,
//secondly because you always write something = malloc(sizeof(*something) ...); so you
//have a good habit.

Using the array:

Any way you choose to declare it (fixed-size or variable-size), you always use an array the same way:

//Either you refer a specific piece:
tab[x] = y; //with x a number (or a variable containing a value inside your array boundaries; and y a value that can fit inside the type of tab[x] (or a variable of that type)
//Example:
int x = 42;
int tab[4]; // An array of 4 ints
tab[0] = 21; //direct value
tab[1] = x; //from a variable
tab[2] = tab[0]; //read from the array
tab[3] = tab[1] * tab[2]; //calculus...
//OR you can use the fact that array decays to pointers (and if you use a variable-size array, it's already a pointer anyway)
int y = 21;
int *varTab;
varTab = malloc(sizeof(*varTab) * 3); // An array of 3 ints
*varTab = y; //*varTab is equivalent to varTab[0]
varTab[1] = x; //Same as with int tab[4];
*(varTab + 2) = 3; //Equivalent to varTab[2];
//In fact the compiler interprets xxx[yyy] as *(xxx + yyy).

Star-ing a variable is called dereferencing. If you don’t know how this works I highly suggest you take a look.

I hope this is explained well-enough. If you still have questions please comment and I’ll edit this answer.