Odd C pointer segmentation fault errors

Question

I am writing a program to split up data entered via command line and put it into separate fields. Right now I am having problems splitting up the data and assigning it to respective pointers. The text file is this:

5, 08:00:00, 2, 60

Where 5 is the patient number, the reading was at 8am, and it is field 2 and he got a 60. I keep getting a segmentation fault error when I run my code, so I put it though gdc and got this, and I think line 88:

*hours = atoi(j);

is messing up:

Welcome to the Health Monitoring System

Program received signal SIGBUS, Bus error. 0x0000000000400826 in get_field ()

This is my code

/*
* Health Monitoring System
*/

#include <stdio.h>
#include <ctype.h>

#define MAXPATIENTS 5
#define MAXREADINGS 10
#define MAXTYPES 5
#define MAXTIME 8

/* One health type reading: timestamp + actual value */
typedef struct{
        char timestamp[MAXTIME+1];
        int value;
}Element;

/* Circular buffer of health type readings */
typedef struct{
        int start;      /* index of oldest reading */
        int end;        /* index of most current reading */
        Element reading[MAXREADINGS];
}CircularBuffer;

/* Patient's health chart: ID + multiple health type readings */
typedef struct{
        int id;
        CircularBuffer buffer[MAXTYPES];
}Chart;


/*
* Health records for all patients defined here.
* The variable record is visible to all functions
* in this file, i.e. it is global.
*/
Chart record[MAXPATIENTS];

void main(){
int i, j;

/* initialize health data records for each patient */

for( i=0; i < MAXPATIENTS; i++ ){
    record[i].id = i + 1;
    for( j=0; j < MAXTYPES; j++ ){
        record[i].buffer[j].start = 0;
        record[i].buffer[j].end = 0;
        }
    }
printf("Welcome to the Health Monitoring System\n\n");

int id;
int hours;
int mins;
int secs;
int field;
int score;
get_field(&id, &hours, &mins, &secs, &field, &score);
printf("%d This is the ID\n", id);
printf("%d This is the hours\n", hours);
printf("%d This is the mins\n", mins);
printf("%d This is the secs\n", secs);
printf("%d This is the field\n", field);
printf("%d This is the score\n", score);

printf("\nEnd of Input\n");
}



int get_field(int* id, int* hours, int* mins, int* secs, int* field, int* score){
        //get the patient ID
        int z = getchar();
        *id = z;
        getchar();
        getchar();

        //this gets the hour

        char j[MAXTIME];
        int m,n = 0;
        while((n=getchar()) != ':'){
                j[m] = n;
                m++;
        }
        *hours = atoi(j);

        //this gets the mins

        char k[MAXTIME];
        n = 0;
        m = 0;
        while((n=getchar()) != ':'){
                k[m] = n;
                m++;
        }
        *mins = atoi(k);

        // this gets the seconds

        char l[MAXTIME];
        n = 0;
        m = 0;
        while((n=getchar()) != ':'){
                l[m] = n;
                m++;
        }
        *secs = atoi(l);

        getchar();
        getchar();

        // this gets the field

        z = getchar();
        *field = z;
        getchar();
        getchar();

        // this gets the score

        m = 0;
        n = 0;
        char x[MAXTIME];
        while ((n=getchar()) != '\n'){
                x[m] = n;
                m++;
        }
        *score = atoi(x);
        return 0;
}

Hi. Asking people to spot errors in your code is not especially productive. You should use the debugger (or add print statements) to isolate the problem, by tracing the progress of your program, and comparing it to what you expect to happen. As soon as the two diverge, then you've found your problem. (And then if necessary, you should construct a minimal test-case.) — Oliver Charlesworth
– Oliver Charlesworth, Commented Apr 27, 2014 at 22:12
It's an array of chars though right? So shouldn't that work? — user3325834
– user3325834, Commented Apr 27, 2014 at 22:14
You've got a whole lot of unterminated char buffers. How about putting some nul terminators in before calling atoi? — Greg Hewgill
– Greg Hewgill, Commented Apr 27, 2014 at 22:15

phyrrus9 · Accepted Answer · 2014-04-27 22:14:43Z

3

I would use scanf instead of running it manually...

 scanf("%d, %d:%d:%d, %d, %d", &field1, &hour, &min, &sec, &field2, &field3);

That would probably clean up some of the problems you are having. Hope that helps.

The problem is, somewhere in that mess of get_field, you are running into an error you don't need to have. scanf uses what are called format strings, meaning they match to a SPECIFIC format and insert data into their respective fields. This takes the pain away from the parsing you are needlessly doing and makes it a lot easier when you can debug the hard stuff instead of trivial stuff like that.

answered Apr 27, 2014 at 22:14

phyrrus9

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5 Comments

gsamaras Over a year ago

Yes, but it wouldn't make the OP understand what he is doing with his pointer. Educate him, don't just give him the code.

phyrrus9 Over a year ago

let me add it to my solution.

phyrrus9 Over a year ago

nothing is wrong with the pointers themselves, its just something else in the function. If you ran it through GDB line by line you could find out where

user3325834 Over a year ago

That also doesn't let me hold on to 00 as a field, it just gives me 0

phyrrus9 Over a year ago

correct. When you print it out, if you printf("%02d:%02d:%02d\n", hours, mins, secs); it will

Paul Roub · Accepted Answer · 2014-04-27 22:17:09Z

1

You're not zero-terminating the strings you're building; atoi() may be reading past the ends of the arrays.

// x will be uninitialized, not necessarily zero-filled
char x[MAXTIME];
while ((n=getchar()) != '\n'){
  x[m] = n;
  m++;
}

x[m] = '\0';    // make it a valid C string

*score = atoi(x);

All of this assumes that we don't get more than MAXTIME characters.

To avoid that problem:

while ((m < (MAXTIME - 1)) && ((n=getchar()) != '\n')){

answered Apr 27, 2014 at 22:17

Paul Roub

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Comments

R Sahu · Accepted Answer · 2014-04-27 22:21:09Z

0

You'll have problems with the following lines:

*hours = atoi(j);

*mins = atoi(k);

*secs = atoi(l);

*score = atoi(x);

since you are not terminating the strings with a null character before calling atoi.

answered Apr 27, 2014 at 22:21

R Sahu

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