How can i put a char pointer into an array char in a for loop in {C}

Question

So my problem is here:

char *input;
char *takenpositions[18] ={"A0","A0","A0" /* etc. */};

int k;

for(k = 0; k < 18; k++) {

  scanf("%s",&input);

  /* ...
     The program is doing other things with input here, then i want to put it
     into the array in place of the A0s. I tried strncpy, and other things but
     maybe i couldn't use it correctly.
     ...
  */

  takenpositions[k] = input;
}

I couldn't find the answer maybe because it's too easy or I'm just lame.

You have not allocated memory for "input". So you can not call "scanf("%s",&input);". If you want to read a string and store it's pointer you have to allocate memory. — MayurK
– MayurK, Commented Oct 22, 2016 at 15:32
@MayurK - and even if memory had been allocated,you wouldn't type &input there, you'd just give the pointer to the memory (which input holds) - passing &input has the effect of passing the address of the variable that holds the address of the available mem. The correct usage would be scanf("%s",input); — enhzflep
– enhzflep, Commented Oct 22, 2016 at 15:36
Please turn up compiler warning level (-Wall -Wextra for gcc and clang), so it warns about bad format strings. Also check return value of scanf to avoid nasty surprises with invalid input. — hyde
– hyde, Commented Oct 22, 2016 at 15:46

MayurK · Accepted Answer · 2016-10-22 16:56:32Z

1

As I mentioned in the comment, you need to allocate memory for "input". Probably this is what you are trying to do.

#define MAX_STR_LEN 256
char *input;
char *takenpositions[18] ={0}; //Initialize all pointers to NULL (0).

int k;

for(k = 0; k < 18; k++) {

    input = malloc(sizeof(char)*(MAX_STR_LEN+1)); //Allocate memory

    char scanfString[32] = ""; //32 characters should be sufficient for scanf string.

    //To limit number of character inputs use string "%<limit>s" in scanf()
    sprintf(scanfString, "%%%us", MAX_STR_LEN);


    scanf(scanfString, input);

  /*
     Your code.
  */

  takenpositions[k] = input; //Save pointer.
}

edited Oct 22, 2016 at 16:56

answered Oct 22, 2016 at 15:37

MayurK

1,9671 gold badge17 silver badges30 bronze badges

Sign up to request clarification or add additional context in comments.

4 Comments

Balázs Sipos Over a year ago

I was trying to do this all afternoon... :D

hyde Over a year ago

Of course with this code, if input is longer than 256 chars, you get buffer overflow. Writing code which may do this is bad, even when just learning C, because bad habits carry over, and double bad when written to Stack Overflow as advice for anyone searching help for similar problem.

MayurK Over a year ago

@hyde Yes. that is the limitation in my answer. I will think about making this answer generic. I will update it soon. Thank you :)

MayurK Over a year ago

@hyde I have modified my answer to allow only limited number of characters in scanf(). I referred stackoverflow.com/questions/1621394/… and stackoverflow.com/questions/3042980/how-to-print-s-in-c links for this change.

Collectives™ on Stack Overflow

How can i put a char pointer into an array char in a for loop in {C}

1 Answer 1

4 Comments

Your Answer

Linked

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

4 Comments

Your Answer

Sign up or log in

Post as a guest

Linked

Related