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cfgetsscanf

input from fgets not stored using sscanf properly

So I have this small part of my code (basically the input for my whole program).

It has to take the form of a string with at most 20 characters, and two integers all separated by a space.

eg master 1 1

int main(void)
{

  int i, x, y;
  char input[28];
  char* name = NULL;
  fgets(input, 28, stdin);
  sscanf(input, "%s %i %i", name, &x, &y);
  printf("%s %i %i\n", name, x, y);
  return 0;
}

Basically I'm trying to print it out to see if the program is storing the input correctly, as it has to be stored in a linked list later on.

Everything worked fine, but no matter what I type, It prints out (null) 0 4196064. It seg faults if I put and ampersand infront of name in the sscanf() function as well.

Any ideas on how to fix this would be much appreciated!

Solution

  • sscanf will not allocate storage for your string.

    char name[28];

    will work. &name causes seg.fault, because that differs in levels of indirection. What you then pass is a char * * , which is interpreted as char * inside sscanf. As your name variable is on the stack, &name points to the stack, so sscanf will overwrite your stack content. That can easily result in a seg.fault.