Printing day for a given date in c using shell script.

Question

I have to print the day for a given date. For example if output is 18 5 2014 , output should be Sunday . I wrote my program like this:

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

int main()
{
    int d,m,y ;
    char command[20];

    printf("Enter d: ");
    scanf("%d",&d);
    printf("Enter m: ");
    scanf("%d",&m);
    printf("Enter y: ");
    scanf("%d",&y);

    sprintf(command , "date -d %d/%d/%d | cut -b 1-3 ",m,d,y );

    system(command) ;
    return 0 ;
}

But output is a little bit scary:

Sat
*** stack smashing detected ***: ./a.out terminated
======= Backtrace: =========
/lib/x86_64-linux-gnu/libc.so.6(__fortify_fail+0x37)[0x7fd1e8d89f47]
/lib/x86_64-linux-gnu/libc.so.6(__fortify_fail+0x0)[0x7fd1e8d89f10]
./a.out[0x400743]
/lib/x86_64-linux-gnu/libc.so.6(__libc_start_main+0xed)[0x7fd1e8ca076d]
./a.out[0x4005a9]
======= Memory map: ========
00400000-00401000 r-xp 00000000 08:05 21758155                           /home/shahjahan/a.out
00600000-00601000 r--p 00000000 08:05 21758155                           /home/shahjahan/a.out
00601000-00602000 rw-p 00001000 08:05 21758155                           /home/shahjahan/a.out
0240d000-0242e000 rw-p 00000000 00:00 0                                  [heap]
7fd1e8a69000-7fd1e8a7e000 r-xp 00000000 08:05 790189                     /lib/x86_64-linux-gnu/libgcc_s.so.1
7fd1e8a7e000-7fd1e8c7d000 ---p 00015000 08:05 790189                     /lib/x86_64-linux-gnu/libgcc_s.so.1
7fd1e8c7d000-7fd1e8c7e000 r--p 00014000 08:05 790189                     /lib/x86_64-linux-gnu/libgcc_s.so.1
7fd1e8c7e000-7fd1e8c7f000 rw-p 00015000 08:05 790189                     /lib/x86_64-linux-gnu/libgcc_s.so.1
7fd1e8c7f000-7fd1e8e34000 r-xp 00000000 08:05 786443                     /lib/x86_64-linux-gnu/libc-2.15.so
7fd1e8e34000-7fd1e9034000 ---p 001b5000 08:05 786443                     /lib/x86_64-linux-gnu/libc-2.15.so
7fd1e9034000-7fd1e9038000 r--p 001b5000 08:05 786443                     /lib/x86_64-linux-gnu/libc-2.15.so
7fd1e9038000-7fd1e903a000 rw-p 001b9000 08:05 786443                     /lib/x86_64-linux-gnu/libc-2.15.so
7fd1e903a000-7fd1e903f000 rw-p 00000000 00:00 0 
7fd1e903f000-7fd1e9061000 r-xp 00000000 08:05 786555                     /lib/x86_64-linux-gnu/ld-2.15.so
7fd1e9249000-7fd1e924c000 rw-p 00000000 00:00 0 
7fd1e925c000-7fd1e9261000 rw-p 00000000 00:00 0 
7fd1e9261000-7fd1e9262000 r--p 00022000 08:05 786555                     /lib/x86_64-linux-gnu/ld-2.15.so
7fd1e9262000-7fd1e9264000 rw-p 00023000 08:05 786555                     /lib/x86_64-linux-gnu/ld-2.15.so
7fffe219c000-7fffe21bd000 rw-p 00000000 00:00 0                          [stack]
7fffe21fe000-7fffe2200000 r-xp 00000000 00:00 0                          [vdso]
ffffffffff600000-ffffffffff601000 r-xp 00000000 00:00 0                  [vsyscall]
Aborted (core dumped)

The output should be only the first line but why I am getting like this? Please help me.

you try to put more than 20 bytes into the command and that might smash your stack — Pavel
– Pavel, Commented May 18, 2014 at 14:47

jahan · Accepted Answer · 2014-05-18 14:52:48Z

1

You should have used proper size for your command string. The below program should work.

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

int main()
{
    int d,m,y ;
    char command[1000];

    printf("Enter d: ");
    scanf("%d",&d);
    printf("Enter m: ");
    scanf("%d",&m);
    printf("Enter y: ");
    scanf("%d",&y);

    sprintf(command , "date -d %d/%d/%d | cut -b 1-3",m,d,y );

    system(command) ;
    return 0 ;


}

answered May 18, 2014 at 14:52

jahan

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Comments

Rafi Kamal · Accepted Answer · 2014-05-18 14:56:24Z

0

The size of the array command is 20. But "date -d %d/%d/%d | cut -b 1-3",m,d,y is more then 20 character long. So you need to increase the size of the command array.

answered May 18, 2014 at 14:56

Rafi Kamal

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