scanf misbehaving...

I'm not sure if I posted this before, sorry if I did. I'm using gcc. The files are attached.

Pretty much whenever I input a really long string (over 20 characters) in the first method grab_string, the second time around a string is automatically inputted whenever I call grab_string_ml. Why is this happening and how can I fix it?

Here's the console info that I have...

Code:

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$ ./main
Input something - > wwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwww
wwwwwwwwwwwwwwwwwwww
Input something - > w

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grab_string_ml() captures the extra 'w' from the buffer in stdin. You can use fflush() to flush the extra input after calling scanf() in grab_string().

Quote:

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Originally Posted by Kheun

grab_string_ml() captures the extra 'w' from the buffer in stdin. You can use fflush() to flush the extra input after calling scanf() in grab_string().

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But I called fflush(stdin); after I called scanf in grab_string_ml(), wouldn't that be enough?

Ok, I just put fflush(stdin); after scanf in grab_string();, no go, same problem persists.

Ok, I tried fgets method, but that still doesn't do what I want (same problem.) I know I had this problem before (and yes I searched the forums before and no I didn't find the answer) but I don't remember how I solved it.

Sorry for the late reply. I haven't been accessing the internet over the weekend.

Quote:

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Originally Posted by YourSurrogateGod

Ok, I just put fflush(stdin); after scanf in grab_string();, no go, same problem persists.

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That's strange. It works for me. See the code below.

BTW, I have made changes to your code as it is giving me warnings. The compiler requires casting the void pointer after calloc. In addition, there is an execuation path in grab_string_ml where it is not returning any value.

Code:

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char * grab_string_ml(int length)
{
 if(length > 0)
 {
  // create a dynamically allocated piece of memory that will store a string of a maximum of length + 1 characters long.
  char * input = (char*)calloc(length + 1, CHAR_BIT);
  // this will hold the middle portion inputted array.
  char middle[5];

  // create the beginning of the string that will be used in oder to input a value into the character array.
  char * beginning = "%";
  // create the ending of the string that will be used in order to input a value into the character array.
  char * ending = "s";
  // create a pointer to a character array that will store the final results.
  char * target = NULL;

  // convert an integer into a character array.
  sprintf(middle, "%d", length);

  // allocate the necessary space for the target.
  target = (char*)calloc(strlen(beginning) + strlen(middle) + strlen(ending) + 1, CHAR_BIT);

  // copy the characters from the beginning into the target.
  strncat(target, beginning, strlen(beginning));
  strncat(target, middle, strlen(middle));
  strncat(target, ending, strlen(ending));

  // have the user input something.
  scanf(target, input);
  // flush the input.
  fflush(stdin);

  // free the allocated memory.
  free(target);

  // return the desired value.
  return input;
 }
 else
 {
  fprintf(stderr, "The inputted value is less than one.\n");
 }

 return 0;    // Added to return a value indicating error.
}

char * grab_string()
{
 // create a dynamically allocated piece of memory that will store a string of a maximum of 21 characters long.
 char * input = (char*)calloc(21, CHAR_BIT);

 // grabe the value from the user.
 scanf("%20s", input);
 fflush(stdin);    // Flushing the input buffer.

 // return the inputted string.
 return input;
}





int main()
{
 // ask the user input something.
 printf("Input something - > ");
 char * value1 = grab_string();
 // output the inputted string.
 printf("%s\n", value1);
 // ask the user input something.
 printf("Input something - > ");
 char * value2 = grab_string_ml(1);
 // output the inputted string.
 printf("%s\n", value2);

 // free the memory.
 free(value1);
 free(value2);

 return 0;
}

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These are the files that I have and this is the output that I'm getting:

Code:

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Using method grab_string_ml.
 Please input a value - > wwwwwwwwwwwww
 Please input a second value - > char1 = wwwww
char2 = www

Using method grab_string.
 Please input a value - >  Please input a second value - > wwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwww
char3 = wwwww
char4 = wwwwwwwwwwwwwwwwwwww

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I give up.

I am very sorry that I couldn't reply earlier as I am quite busy with my work nowadays.

I have made some changes to your code in order to compile and handles memory leak. Everything else works fine on VC7.

Code:

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// In custom_input.c
int grab_int_ml(int length)
{
 if(length > 0)
 {
  // create an array of characters that will be used to store an input as a
  //  string, from which the integer will be taken out of.
  char input[255];  // Must be a constant value.

  // this will hold the middle portion inputted array.
  char middle[5];

  // create the beginning of the string that will be used in oder to input a
  //  value into the character array.
  char * beginning = "%";
  // create the ending of the string that will be used in order to input a
  //  value into the character array.
  char * ending = "s";
  // create a pointer to a character array that will store the final results.
  char * target;


  // convert an integer into a character array.
  sprintf(middle, "%d", length);

  // allocate the necessary space for the target.
  target = calloc(strlen(beginning) + strlen(middle) + strlen(ending) + 1,
  CHAR_BIT);

  // copy the characters from the beginning into the target.
  strncat(target, beginning, strlen(beginning));
  strncat(target, middle, strlen(middle));
  strncat(target, ending, strlen(ending));

  // have the user input something.
  scanf(target, input);

  // free allocated resources.
  free(target);

  // convert the string to an integer and return it.
  return atoi(input);
 }
 else
 {
  fprintf(stderr, "The inputted value is less than one.\n");
 }

 return 0;
}


// In main.c
int main()
{
  // Only in C, declaration must comes first before the rest of the function.
  char *char1, *char2, *char3, *char4;

 /*printf("Using method grab_int_ml.\n");
 printf(" Please input a value - > ");
 int val1 = grab_int_ml(2);
 printf(" Please input a second value - > ");
 int val2 = grab_int_ml(3);
 printf("val1 = %d\nval2 = %d\n\n", val1, val2);
 printf("Using method grab_int.\n");
 printf(" Please input a value - > ");
 int val3 = grab_int();
 printf(" Please input a second value - > ");
 int val4 = grab_int();
 printf("val3 = %d\nval4 = %d\n\n", val3, val4);*/

 printf("Using method grab_string_ml.\n");
 printf(" Please input a value - > ");
 //char * char1 = grab_string_ml(5);
 char1 = grab_string_ml(5);
 printf(" Please input a second value - > ");
 //char * char2 = grab_string_ml(3);
 char2 = grab_string_ml(3);
 printf("char1 = %s\nchar2 = %s\n\n", char1, char2);
 //Releasing memory.
 free(char1);
 free(char2);

 printf("Using method grab_string.\n");
 printf(" Please input a value - > ");
 //char * char3 = grab_string();
 char3 = grab_string();
 printf(" Please input a second value - > ");
 //char * char4 = grab_string();
 char4 = grab_string();
 printf("char3 = %s\nchar4 = %s\n\n", char3, char4);
 //Releasing memory.
 free(char3);
 free(char4);

 return 0;
}

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Here's my output.

Code:

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Using method grab_string_ml.
 Please input a value - > wwwwwwwwwwwwwwwwwwwwww
 Please input a second value - > ssssssssssssssssssssssss
char1 = wwwww
char2 = sss

Using method grab_string.
 Please input a value - > dddddddddddddddddddddddddddddddddddddddddddd
 Please input a second value - > eeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeee
char3 = dddddddddddddddddddd
char4 = eeeeeeeeeeeeeeeeeeee

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