Thread: segmentation fault with strtod

Hey guys im making a clock program which the user enters the time. However if the user types say 3 45 why am i getting a segmentation fault. Im using strstod it gets the start of the input 3 for the hour. But for m it will store say 40 instead of 45 so its not converting properly. Not sure why ? Could this be the cause of the seg fault?

Code:

int getClockInput(int optionStats[NUM_OPTION_STATS])
{
    int h, m;
    int display_error, end_of_input;
    char *start;
    char *end;

    printf("\nEnter <hours> <minutes>: ");

    fgets(start, MAX_CHAR, stdin);
    h = (int) strtod(start, &end);
    m = (int) strtod(end, &end);

    if(start[strlen(start)-1] !='\n')
    {
          readRestOfLine();

    }
    else
    {
      start[strlen(start)-1] = '\0';
    }
    /*scanf("%d%d", &h, &m);*/
    display_error = displayClock(optionStats,h, m);
    
    if (display_error)
    {
      printf("Incorrect data received for hours and minutes\n");
      return 0;
    }

    return 0;

}

You didn't point start to an array or malloc'd memory, it's uninitialized.

would i do something like this char *start[SIZE]

That'd give you an array of pointers, so you'd probably rather have this:

Code:

char start[MAX_CHAR];

Yep thats right. Is there anything else i need to change i still get a seg fault?

This is the other portion of the code in another file gdb shows a seg fault when it updates the clock with hr and hs symbolds with the outter and inner for loop. Not sure why?

Code:

int displayClock(int * optionStats, int h, int m)
{
    char clock[9][20] = { /* The array to hold the hard-coded clock */
        "        12         ",
        "   11        01    ",
        " 10            02  ",
        "                   ",
        "09      .       03 ",
        "                   ",
        " 08            04  ",
        "   07        05    ",
        "        06         "
      };

	/* Row and column numbers in clock array for hour positions. For
	 * example, the "06" in the clock display is stored at position
	 * [8, 8] in the clock matrix (see above) */
    const int hr[13] = {0, 1, 2, 4, 6, 7, 8, 7, 6, 4, 2, 1, 0};
    const int hc[13] = {0, 13, 15, 16, 15, 13, 8, 3, 1, 0, 1, 3, 8};

	/* Hour and minute codes */
    const char hs = 'H', ms = 'm';

    int i, j; /* Declare other variables as needed */
    int a, b;
	/* The next 5 comments require code to be developed by you! */

	/* Ensure that h and m are in range and, if not, return
	 * appropriate error value. Otherwise adjust h if it is 0 or it
	 * exceeds 12
	 */
     if(h>12 || h<1)
     {
            printf("Hours is invalid 1 - 12\n");
            return FALSE;
     }
         

     if(m<0 || m>=60)
     {
            printf("Minutes is invalid 0 - 60\n");
            return FALSE;
     }
         
    /* Now update the clock array accordingly, with the hour symbol */

	/* Round m to the nearest hour position */

	/* Update clock with minute symbol, taking into account a "clash"
	 * with the hour symbol 
	 */
          for(a=0; a<9; a++)
        {
        
          for(b=0; b<19; b++)
          {
                 clock[hr[h]][hc[h]] = hs;
                 clock[hr[h]][hc[h]+ 1] = hs;
               
              
                  
                
               
           }
                 
                 clock[hr[m]][hc[m]] = ms;
                 clock[hr[m]][hc[m]+ 1] = ms;
         }     

    
	/* Display the clock */
    for (i = 0; i < 9; i++)
    {
        for (j = 0; j < 19; j++)
    	    printf("%c", clock[i][j]);
        printf("\n");
    }
    printf("\n");

    return 0;
}

well you need to tokenize the string first to get the hours and min seperate. And then you need to convert them into double using strtod.

use sscanf to tokenize the sting and you can convert then into float as well.

Code:

#include<stdio.h>

int main()
{
    char str[]="3 45";
    float h, m;
    
    sscanf(str,"%f %f",&h,&m);
    
    printf("%f %f",h,m);
    
    getchar();
    return 0;
}

ssharish2005

i cant use anything else but fgets by the way

well, it was just an exmple to show you how to use sscanf. If u are restricted to fgets then get the input through fgets and then tokenize the string through sscnaf, rather than strtod.

Or if you still need to use strtod, allocate memory for both start and end char pointer. And the send then as a parmater to the strtod function.

It was giving sef fault becuase u allocated memory for start but not for end

Code:

start = malloc (20);
end  = malloc (10);

ssharish2005

Ok just another question how come your using strtol instead of strtod?

Hey guys i have changed it to what Salem said to do and i still get a seg fault and when i run the debugger it always seems to point to the code below

clock[hr[m]][hc[m]] = ms;
clock[hr[m]][hc[m]+ 1] = ms;

maybe im accessing part of the array which isnt there in the for loop im not sure?

But i checked the values of m and h and they are being correctly seperated for hours and minutes now with strol working with it. But still getting seg fault not?

Code:

  for(a=0; a<9; a++)
        {
        
          for(b=0; b<19; b++)
          {
                 clock[hr[h]][hc[h]] = hs;
                 clock[hr[h]][hc[h]+ 1] = hs;
               
              
                  
                
               
           }
                 
                 clock[hr[m]][hc[m]] = ms;
                 clock[hr[m]][hc[m]+ 1] = ms;
         }

Within your loop, m (which stands for minutes) goes from 0 to 59, yet your array hc is of size 13. The access hc[m] accesses illegal memory. The same goes for hr[m].

And why is your loop body completely independent of a and b ?