print sqlite3_exec error message cause segmentation fault in C

Question

I use sqlite3 in C with ubuntu 14.04. In my process I update the db every 20 minutes.

Here is my function :

int update_alive_state(uint64_t ieee,bool isAlive)
{
    char *error_report = NULL;
    char sql[100];
    int result = -1;
    UpdateAliveStateSql(sql,ieee,isAlive);
    if(result = sqlite3_exec(db_event, sql, 0, 0, &error_report))
    {
        printf( "\t> CMD: %s , Error: %s\n" , sql , error_report );
        sqlite3_free(error_report);
    }

    return result;
}

When sqlite3_exec() return error and print error message, I get the segmentation fault message and the process terminated.

ERROR: signal 11 was trigerred:
  Fault address: 0xae703f1b
  Fault reason: address not mapped to object
Stack trace folows:
./main.bin(segmentation_fault_handler+0xd5)[0x419e9f]
/lib/x86_64-linux-gnu/libpthread.so.0(+0x10330)[0x7fa386f20330]
/lib/x86_64-linux-gnu/libc.so.6(_IO_vfprintf+0x1d03)[0x7fa386257943]
/lib/x86_64-linux-gnu/libc.so.6(_IO_printf+0x99)[0x7fa3862603d9]
./main.bin(update_alive_state+0x15d)[0x43ca78]
./main.bin(EventScanThread+0x2af)[0x442c21]
/lib/x86_64-linux-gnu/libpthread.so.0(+0x8184)[0x7fa386f18184]
/lib/x86_64-linux-gnu/libc.so.6(clone+0x6d)[0x7fa38630637d]
Executing original handler...

If I comment out printf and sqlite3_free, segmentation fault message would be disappeared. Why can I not print the error message?

Please help me.

Edit: I changed my code like this

if(result = sqlite3_exec(db, sql, 0, 0, &error_report))
{
    printf( "[ERR] : \t> CMD: %s , Error: %d\n" , sql , result );
    if ( error_report )
    {
        printf( "[ERR] : Error msg: %s\n", error_report );
        sqlite3_free(error_report);
    }
}

But I still get a segmentation fault message.

ERROR: signal 11 was trigerred:
  Fault address: 0x7f3dc490cf1b
  Fault reason: address not mapped to object
Stack trace folows (partial):
./main.bin(segmentation_fault_handler+0xd5)[0x419e9f]
/lib/x86_64-linux-gnu/libpthread.so.0(+0x10330)[0x7fab749ac330]
/lib/x86_64-linux-gnu/libc.so.6(_IO_vfprintf+0x1d03)[0x7fab73ce3943]
/lib/x86_64-linux-gnu/libc.so.6(_IO_printf+0x99)[0x7fab73cec3d9]
./main.bin(update_last_receive_time+0x166)[0x43d60e]
./main.bin(attr_process_attribute_report_ind+0x97)[0x4222dc]
./main.bin(si_gateway_incoming_data_handler+0xa3)[0x41b6b1]
./main.bin(tcp_socket_event_handler+0x558)[0x41c316]
./main.bin(polling_process_activity+0xde)[0x41a4e1]
./main.bin(main+0x150)[0x41a0f4]
Executing original handler...

The error address points to the first printf function

printf( "[ERR] : \t> CMD: %s , Error: %d\n" , sql , result );

Why? Please help me. Thanks.

And if you catch the crash in a debugger, what is the value or error_report? Is it perhaps a null pointer? — Some programmer dude
– Some programmer dude, Commented Jul 3, 2017 at 8:28
sqlite3_exec expects a double pointer to a char as last parameter, but you're printing it (error_report) as if it was a normal string. — Federico klez Culloca
– Federico klez Culloca, Commented Jul 3, 2017 at 8:29
@FedericoklezCulloca The sqlite3_exec function expected a pointer to a pointer (to char) as a way to emulate pass-by-reference, so it can set the original pointer to point to a string. And the OP is passing the correct thing to sqlite3_exec (a pointer to a pointer to char) and since it should be a string it is printed as a string which is also correct. The problem is probably, as I mentioned in my previous comment, that there is no error message and sqlite3_exec leaves error_report as a null pointer. — Some programmer dude
– Some programmer dude, Commented Jul 3, 2017 at 8:36
Thanks @Some programmer dude , I suppose every sqlite3_exec() error code has error message. I will try to check if (error_report) is NULL or not. — Frazier Chang
– Frazier Chang, Commented Jul 3, 2017 at 8:50

Andre Kampling · Accepted Answer · 2017-07-27 07:14:09Z

2

The documentation states:

If the 5th parameter to sqlite3_exec() is not NULL and no errors occur, then sqlite3_exec() sets the pointer in its 5th parameter to NULL before returning.

So it is possible that there is no error messsage at all and you should do:

if (result = sqlite3_exec(db_event, sql, NULL, NULL, &error_report))
{
   if (error_report)
   {
      printf( "\t> CMD: %s , Error: %s\n" , sql , error_report );
      sqlite3_free(error_report);
   }
}

to check if it was set to NULL.

I changed my code like this [...]
But I still get segmentation fault message. [...]
The error address points to the first printf function:
printf( "[ERR] : \t> CMD: %s , Error: %d\n" , sql , result );

If you print a character array with %s, printf needs a null terminated '\0' C-string. As you dont provide your UpdateAliveStateSql function I can't see if the sql string is null terminated. To ensure that by writing a '\0' at the end of the buffer you could do:

sql[sizeof(sql) - 1] = '\0';

after calling the UpdateAliveStateSql function.

edited Jul 27, 2017 at 7:14

answered Jul 3, 2017 at 8:36

Andre Kampling

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2 Comments

Frazier Chang Over a year ago

Thanks @Andre Kampling , I will try then.

Andre Kampling Over a year ago

@FrazierChang: I extend my answer as I saw that you edited your question. Please tell the status.

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