How to read string from keyboard using C?

Question

I want to read a string entered by the user. I don't know the length of the string. As there are no strings in C I declared a pointer:

char * word; 

and used scanf to read input from the keyboard:

scanf("%s" , word) ; 

but I got a segmentation fault.

How can I read input from the keyboard in C when the length is unknown ?

Answer 1

You have no storage allocated for word - it's just a dangling pointer.

Change:

char * word; 

to:

char word[256]; 

Note that 256 is an arbitrary choice here - the size of this buffer needs to be greater than the largest possible string that you might encounter.

Note also that fgets is a better (safer) option then scanf for reading arbitrary length strings, in that it takes a size argument, which in turn helps to prevent buffer overflows:

 fgets(word, sizeof(word), stdin); 

Answer 2

I cannot see why there is a recommendation to use scanf() here. scanf() is safe only if you add restriction parameters to the format string - such as %64s or so.

A much better way is to use char * fgets ( char * str, int num, FILE * stream );.

int main() {     char data[64];     if (fgets(data, sizeof data, stdin)) {         // input has worked, do something with data     } } 

(untested)