how to fix this error and why am I getting it?

Question

i need to convert time in 12 hr to the 24 hr format.

ive hardcoded the 12 hour time for now to make stuff simpler.

my logic: input sting 07:05:45PM extract last 2 chars. if AM check is first 2 chars are 12.. if yes chance them to 00 else output as it is if PM check if first 2 digits are 12 ..if yes leave as it is if not then add 12 to first 2 digits

    #include<stdio.h>
    #include<stdlib.h>
    #include<string.h>

    char* timeConversion(char* s1)
    {
        // input sting 07:05:45PM
        // extract last 2 chars.
        // if AM 
        // check is first 2 chars are 12.. if yes chance them to 00
        // else output as it is
        // if PM 
        // check if first 2 digits are 12 ..if yes leave as it is
        // if not then add 12 to first 2 digits

        char s[strlen(s1) + 1];
        strcpy(s, s1);


        char suffix[3]; // pm am 
        suffix[0] = s[strlen(s) - 2];
        suffix[1] = s[strlen(s) - 1];
        suffix[2] = '\0';

        char xx[3]; // first 2 nos
        xx[0] = s[0];
        xx[1] = s[1];
        xx[2] = '\0';

        s[strlen(s1) - 1] = '\0';
        s[strlen(s1) - 2] = '\0';

         if(strcmp(suffix, "AM") == 0)
        {
            if(strcmp(xx, "12") == 0)
            {
                s[0] = '0';
                s[1] = '0';
                strcpy(s1, s);

             }
             else
            {
                return s1;
            }
        }
        else
        {


            if(strcmp(xx, "12") == 0)
            {
                strcpy(s, s1);
                return s1;
             }
            else
            {
                int n;
                // 01 - 09 
                if(xx[0] == '0')
                {
                    char x = xx[1];
                    n = x - '0';

                    // xx = itoa(n);
                }
                else
                {
                    // 10, 11
                    n = atoi(xx);

                }
                n = n + 12;



                 // itoa(n, xx, 10);
                sprintf(xx, "%d", n); 
                s[0] = xx[0];
                s[1] = xx[1];
            }
        }
        strcpy(s1, s);
        return s1;   
    }  

    int main()
    {
       char *str = "07:05:45PM";
       char *str1 = timeConversion(str);
       printf("%s\n", str1);
       return 0;

    }

Bus error: 10 is what im getting on running the code

You are not allowed to change `s1` inside the function as `str` points to a string literal which is a constant. You can try: `char *str = "07:05:45PM";` ==> `char str[] = "07:05:45PM";` but I'm not sure it solves all problems. — Support Ukraine, May 21 '19 at 08:26
"_ive hardcoded the 12 hour time for now to make stuff simpler._" : Unfortunately that is exactly what has caused your problem! — Clifford, May 21 '19 at 08:45
Since I wrote it before the close, you might as well get the benefit, [12 Hour Time to 24 Hour Time](http://susepaste.org/83039052) expires: Tue May 28 15:49:54 CDT 2019 — David C. Rankin, May 21 '19 at 08:50

score 0 · Accepted Answer · answered May 21 '19 at 08:26

The problem is in

 strcpy(s1, s);

you're essentially trying to write into a pointer to the first element of a string literal. It invokes undefined behaviour.

Check the function call

timeConversion(str);

where str points to a string literal, and any attempt to modify the contents of a string literal is UB.

What you need to do in timeConversion() function is to:

have required amount of memory allocated (call to malloc() is one way)
use that to hold the modified output
return the pointer to the caller.
free the memory once you're done using it.

how to fix this error and why am I getting it?

1 Answers1